JPH02280693A - Driving system for pwm inverter in three-phase motor - Google Patents

Abstract

PURPOSE:To obtain a wide phase voltage range by a method wherein respective transistors of an inverter are controlled so as to be put ON/OFF by the outputted ON/OFF switching time of respective phases. CONSTITUTION:The ON/OFF switching times of the inverter switching elements QW1, QW2 of W-phase are fixed in a constant condition during a pulse width modulating period by the commanding voltages of U-phase and V-phase, for example, while the ON/OFF switching time of the U-phase and the V-phase are obtained based on the fixed ON/OFF switching time of the W-phase. The ON/OFF controls of the inverter switching elements QU1, QU2, QV1, QV2, QW1, QW2 of the U-phase and the W-phase are effected by the obtained ON/OFF switching times of the U-phase and the V-phase. According to this method, a wide phase voltage range may be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to PWM (pulse width variable UA) in three-phase electric
) Regarding the RIJH method.

Conventional technology PWM inverter control systems for three-phase motors include drive switching elements such as bipolar transistors and power MOSFETs for passing current through the windings of each phase, and these switching blocking devices are turned on and off. control,
The PWM 1111 IIi method for driving a three-phase electric motor is adopted.

In the PWM it, IJ ill method, since the switching elements of the inverter are turned on and off, each terminal voltage of the three-phase electric VJ machine can only take two values.

Figure 10 shows the electrical configuration of a three-phase motor.
In the conventional PWM inverter control method for a three-phase motor, the voltage N at the neutral point is assumed to be OV, and the on/off time of the inverter switching element of each phase is determined based on the command voltage of each phase.

For example, if the triangular wave is a sawtooth wave as shown in FIG. 3, each terminal voltage Vl, V2 . V3 is the fourth
As shown in Figures (a) to 4(C), the power supply voltage ±3r
Takes two values. Therefore, each terminal voltage V1. V2. V3
The phase voltages u, VV, and VW corresponding to the average voltage of are determined by the following equation (1).

V i = (Br-T i -Br (Tc-T i
))/Tc= (Br/Tc)(2Ti-Tc)
-<1) In equation (1), Vi=,
Vu, Vv.

Vw, T i is u, V, W phase + 7) da/ffi pressure V
1. V2゜■3 becomes + [3r period Tu, Tv, T
w, and TC is one cycle time of the PWM sawtooth wave.

From the above equation (1), From the above equation (2), When the command voltages vu, VV, and VW of each phase are given, the inverter switching elements of each phase are turned on.

The off-switching time 7u, TV, and TW are determined independently,
The inverter switching elements of each phase are turned on and off during this on/off switching time.

Problems to be Solved by the Invention In equation (1), since 0≦Ti≦TC, the phase voltage Vi (=Vu, Vv, Vw) of each phase is -3r≦Vi
It falls within the range of ≦→−Br. For example, when the power supply voltage ±Br is ±100V and 7u and Tv are changed to O-Tc, the phase voltage of U phase Vu= (Br-/T
c) (2Tu-Tc>, V phase voltage Vv= (B
r/Tc)(2Tv-Tc)(1') When the voltage region is mapped, it changes in the region within the broken line 50 in FIG. 7, and each phase voltage Vu.

VV, VW) can only output a maximum of ±100V (=Br).

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a PWM inverter drive method that can obtain a wider phase voltage range than the conventional methods described above.

Means for Solving the Problems The present invention determines a phase that fixes the on/off switching time of an inverter switching element of one phase to one state during a PWM cycle from the command voltages of two phases, and calculates the phase of the fixed phase. By determining the on/off switching time of the other two phases based on the on/off time and turning on/off the inverter switching elements of each phase based on the found on/off switching time of each phase, it is possible to The phase voltage region was obtained.

Function In the conventional method, the on/off switching time of the inverter switching elements of each phase was determined by assuming that the voltage N at the neutral point was 0. However, in reality, the voltage N at the neutral point was It fluctuates without any change.

For example, as shown in FIGS. 4(a) to 4(C), U
, V, W phase inverter switching element on/off switching times are Tu, Tv, Tw, the voltage at the neutral point N
is a voltage expressed by the following equation (3).

N= (Vl +V2+V3)/3...
-(3) Figure 5 shows the voltage N at this neutral point.

Phase 1 of each phase is the difference between this neutral point voltage N and each terminal voltage.
Pressure Vu (=V1-N), Vv (==V2-N), V
Melt w (=V3-N), Figure 6 (a) - 6
The state shown in Figure (C) is reached.

Therefore, when calculating the average voltage of each phase, the following (4) 2~
It becomes as shown in Equation (6).

Vu-Vl-N=(2Br/3Tc)(2Tu-Tv-
Tw)...(4) Vv-V2-N-(2Br/3Tc)(-Tu+2Tv
-Tw)...(5) Vw=V3-N= (2Br/3Tc)(-Tu-Tv
+27w)...(6) According to equations (4) to (6) above, the on/off switching time u of the inverter switching element of each phase is calculated from the command voltages vu, vv, and vw of each phase. , 7v.

All you have to do is find TW, but the equation (6) is obtained by adding the above equations (4) and (5).
= VW), there are 3 unknowns (Tu, Tv, Tw) - r equation becomes 2 equations, so the conditions are insufficient, and the above (4) 2nd to 3rd (
6) On/off switching time Tu can be determined from the formula alone.

Tv and Tw are not required.

Therefore, assuming that the on/off switching time of one phase is known, for example, assuming that the on/off switching time Tw of the W phase is known, the other phase's When the on/off switching time is determined, the following equations (7) and (8) are obtained.

Tu=Tw+ (Tc/2Br)(2Vu+Vv)・
... (7) Tv=Tw+ (Tc/2B r) (2Vv+Vu
)... (8) Tatashi, Dingw=echi, Vw=-Vu-vwr.

Generalizing the above equations (7) and (8), we get the following (
9) Equation becomes.

Ti=Tj+ (Tc/2BrH2Vi+Vk)...
... (9) However, 7i is the ON state of the desired phase (U, V, W).

OFF l, 77 switching time (=Tu, Tv, Tw), Tj is the on/off switching time of the known phase, vi is the phase voltage of the desired phase, Vk is the phase voltage other than the desired phase and the known phase. It is B.

In the above equations (4) 2 to (6), 0 ≦ Tu, Tv, Tw ≦ Tc, so 4Br/3Tc≦Vu, Vv, Vw≦4Br/3TC, and the phase voltage of each phase is ± the power supply voltage. Voltage g higher than 3r
This shows that it is possible to take the A range.

Therefore, the on/off switching time Tj of one phase is fixed,
Set Tj = CL or Tj = Tc, and change the fixed phases to U-W phases in sequence (Tj = 7u, TV, TW).
, and other phases, the voltages of the positive and -phase phases within the solid line 51 in FIG. 7 are obtained, and it can be seen that a wider voltage range can be obtained compared to the conventional method. In addition, in FIG. 7, electric 11! The voltage ±Br is set to ±100V.

In addition, FIG. 8 shows ON in the voltage region shown in FIG. 7 above.

This shows a phase relationship in which the off-switching time Tj is fixed to "0" or rTcJ. As shown in Fig. 8, the areas of the fixed on/off switching times Tj overlap, so in order to eliminate the switching error of the fixed on/off switching times Tj, the fixed on/off switching times Tj are added as shown in Fig. 9. The phase of the on/off switching time Tj to be determined is determined.

As a result, if the command voltages of two phases are given, in this example, if the command voltages Vu and Vv of the positive phase and the ■ phase are given,
The on/off switching time is 0 or T based on these two command voltages.
The phase to be fixed to C is determined, and other on/off switching times are determined from equation (9).

For example, in FIG. 9, if vu≧O, VV≧0, then
The on/off switching time TW of the W phase is rOJ, and Vu<O
, if Vv<O, the W phase is turned on.

Fix the off switching time to TW@TC. Also, vu≧o,
When vv<o, if vu≧−Vv, the U phase on/off switching time lower U is set to Tc, and if Vu<−VV, the V phase on/off switching time Tv is set to 1−OJ. Also, V
When u<O, Vv≧0, if VV≧−Vu, the on/off switching time TV of the ■ phase is Tc, and if VV<−VU, the on/off switching time Tu of the U phase is rOJ. and fix it.

And on with fixed on, off switching times.

Using the other two command voltages for which the off-switching time is not fixed, calculate the on-off switching time Ti of the other two phases by calculating the equation (9), and then switch the inverter switching element. .

For example, the electric 8Q voltage ±Br is ±100V and the U phase.

■If the phase command voltage Vu is 60V and tJv is -100V, Vw--(Vu+Vv)=-(60-100)=
40V! : becomes, Vu>O, Vv<OF, and Vu
< -V-V, so from Figure 9 it becomes TV-〇, and from equation (9), Tu=Tv+ (Tc/2BrH2Vu+Vw)=O+
(Tc/200) (2x60+40>-(160/2
00)-Tc =4Tc15 Tw-Tv+ (Tc/2BrH2Vw+Vu)-O+
(Tc/200H2x40-t60)=(14
0/200)・Tc=7・TC/10, and the inverter switching elements of each phase are turned on.

The off-switching time is determined.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention.

In Figure 1, 10 is a three-phase AC power supply, 12 is a rectifier circuit, and 14
1 is a smoothing capacitor, 16 is a control circuit for regenerative current, 18 is an inverter composed of transistors, diodes, etc., 20 is a current detector, 22 is a three-phase motor, 2
4 is a pulse rotor for detecting the position and speed of the rotor of the electric motor 22; 26 is a receiver circuit; 28 is a rotor position detection circuit; 30a and 30b are gate devices; ■Phase current command Iuc,
lvc is obtained, and the actual current Ju of the U phase and ■ phase is detected by the current detector 20 from these current commands.

[The process is the same as the conventional method until the current deviations of the U phase and 2V phases are obtained by subtracting V, respectively, and the voltage commands of the U phase and ■ phase are obtained from these current deviations.

The present invention creates a PWM signal using a processor such as a jig-pull processor. Conventionally, it is well known that the position, speed, and current control 11 is performed by a processor. Control circuit 4o
It consists of Then, the PWM signal output from the PWM control circuit 40, that is, the transistor Qu1.
Qu2.

The driver 38 is driven by the on/off switching times TLJ, TV, and TW of Qvl, Qv2, QwY, and 0w2, and the transistors Qu1 . Qv1.

On/off switching time Tu outputted from Qwl.

Only TV and TW are turned on, and the other transistor Qu2 is turned on.
, Qv2.0w2 is turned off. Turning on and off of this transistor is the same as in the conventional case.

That is, depending on the torque command value IC and the rotor position, U
Determine the current commands 1uc and Ivc for the phase and ■phase, subtract the actual currents IU and IV from these current commands 1uc and Ivc, respectively, to determine the current deviation (IuC-1u) (Ivc-Iv), and calculate this current deviation () UC -ItJ) and <IVC-IV), the process is the same as the conventional process until the command voltage of the U phase and vll is determined.

However, this command voltage turns on the PWM signals of each phase, that is, the transistors of each phase of the inverter.

The present invention differs from conventional approaches in creating an off-switch time.

The processor of the PWM&II control circuit 40 executes the process shown in the flowchart of FIG.
It is executed every II cycle Tc, and when the command voltages Vu and Vv of the U phase and the and obtain the W-phase command voltage VW (step S1).
It is determined whether the command voltage Vu of the phase is 0 or a positive value (step S2), and if it is 0 or more, it is determined whether the command voltage Vr of the V phase is O or a positive value (STELLA 7s3), Vu≧O,
If Vv≧Or, set the W-phase PWM signal, that is, the on/off switching time TW of the W-phase switching element to rOJ (step 59) (see FIG. 9), and take this on/off switching time Tw as rOJ. ■The (9th) phase command voltage Vu, Vv
) is calculated to find the on/off switching times Tu and Tv of the other U-phase and ■-phase (step 814). Then, step S9. On/off switching time T determined in S14
In step 816), the driver 38 is driven to output the transistors Qu1, QV of each phase.
On/off switching time Tu, T outputted from l, Qwl
Turn on only v and TW, and turn on the other transistor Qu2.
, Qv2.

Turn off 0w2 respectively. Then, the remaining time of the PWM cycle TC (Tc-Tu), (Tc-Tv) (Tc-Tw
) are transistors Qu1 and Qvl.

Qwl are turned off, transistors Qu2 . QV2゜0w
2 are turned on.

On the other hand, if Vu≧O and VV<0, step 82.8
3) It is determined whether the command voltage Vu of the LJ phase is larger than the command voltage of the V phase with its sign inverted (VU>-VV).Step S4) If Vu≧-VV, (J Set the phase on/off switching time Tu to the PWM cycle IIQTc (step $7) (see Figure 9).Then, from this on/off switching time Tu and the command voltages of the ■ phase and W phase, the
9) Calculate the equations to find the on and off switching times Tv and Tw of the V and W phases (step 513), and output the found on and off switching times Tu, Tv and Tw (step 516). , the driver 38 turns on and off each transistor of the inverter 18 as described above.

Furthermore, if it is determined in step S4 that Vu<-VV, ■
Set the phase on/off switching time TV to 1°0 (step 58) (see Figure 9), and set the phase (9
) and performed the U-phase.

The on/off switching times Tu and Tw of the W phase are determined (step 515), and the 1 and 7J1% time periods u, TV, and TW are outputted (step 816).

Further, in step S2, it is determined that Vu<O, and VV<0
When it is determined that (step S5), the W phase is turned on,
Step 8: Set the off switching time TW to l'TcJ.
10) (see Figure 9), proceed to step S14, and
, Vu, vv to calculate the on/off switching times Tu, Tv, and calculate Tu, Tv, Tw.
is output (step $16).

Further, if it is determined that VLI<O (step 82), Vv≧0 (step S5), and v■≧−vU (step S6), step 511), the process proceeds to step S15, and the on/off switching times Tu and Tw of the U and W phases are determined, and each switching time Tu is obtained.

Outputs TV and TW.

Furthermore, if it is determined in step S6 that Vv<-Vu, then U
Set the phase on/off switching time TU to 10".
512), the process moves to step S13 and the on/off switching time TV of the U and W phases is determined.

Tw is determined and the switching times Du, Tv, and Tw are output.

In this way, the output on/off switching time Tu of each phase,
Tv and Tw drive the driver 38, turn on and off each transistor of the inverter 18, and control the drive of the three-phase motor 22.

Effects of the Invention In the present invention, since the PWM signal (ON/OFF switching time) is created by taking into account the voltage at the neutral point, a wider phase voltage range can be obtained compared to the conventional system, and the response can be improved. A good three-phase motor is obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a flowchart of processing performed by the processor of the PW M 1II control circuit in the same embodiment, and FIG. 3 is a block diagram of an embodiment of the present invention.
Diagrams showing sawtooth waves of WM, Figures 4(a) to 4(C)
) is an example showing the state of each terminal voltage of a three-phase electric motor, Fig. 5 is an example showing the state of the neutral point of a three-phase motor, Fig. 6 (a)
- Fig. 6 (C) is an example showing the state of each phase voltage, Fig. 7 is an explanatory diagram showing the phase voltage regions of the U phase and ■ phase according to the conventional method and the method of the present invention, Figs. 8 and 9 The figure is an explanatory diagram showing the relationship with the phases that fix the on/off switching time in the U-phase and ■-phase voltage regions, and FIG. 10 is a diagram showing the electrical configuration of the three-phase motor. 10... Three-phase AC power supply, 12... Rectifier circuit, 18.
... Inverter, 22... Three-phase motor, 24... Pulse loader, 30a, 30b... Multiplier, 38...
Driver, 40... PWM control circuit, 50... Voltage domain according to conventional method, 51... Voltage domain according to the present invention. 〉

Claims (1)

[Claims] In the drive method of a PWM inverter in a three-phase motor, the phase that fixes the on/off switching time of the inverter switching element of one phase in one state during the PWM cycle is determined from the command voltages of two phases, and the phase of the fixed phase is determined. Based on the on and off times, calculate the on and off switching times of the other two phases,
A driving method for a PWM inverter in a three-phase motor, characterized in that an inverter switching element of each phase is turned on and off according to the determined on/off switching time of each phase.