JPH02211084A - Inverter device - Google Patents

Abstract

PURPOSE:To suppress a transient torque by repeating two switching modes at the time of DC braking to equalize the phase of the vector of a composite output voltage of an inverter main circuit to the voltage phase at the time of start of the DC braking. CONSTITUTION:An AC power source 12 is converted to a DC by a converter 13, and inverted by an inverter 14. Six transistors(Tr) QU-QW and QX-QZ for forming an inverter main circuit 11 are turned ON, OFF in six sets of switching modes by a controller 15 and a base amplifier 16 to generate 3-phase VVVF, thereby rotating a motor 17. When a braking command SB is input to the controller 15, the controller 15 repeats two switching modes to equalize the vector phase of the composite output voltage of the inverter main circuit 14 to the voltage phase at the time of start of DC braking. Thus, variations in a transient torque are suppressed to perform a smooth braking.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an inverter device capable of performing DC braking of an electric motor.

(Prior Art) For example, a three-phase voltage source inverter device generally has a switching element group 1 consisting of six transistors as shown in FIG.
The configuration is such that AC power is supplied to a motor 2 as a load by sequentially switching the switching mode of the switching element group 1. In order to perform DC braking of the electric motor in such a configuration, when a braking command is given, the switching element group 1 is fixed in a predetermined switching mode and DC is applied to the windings of the electric motor 2.

By the way, in this type of inverter device, except for the IPIi type switching mode in which all transistors are turned off, the only meaningful switching mode is 6 Pl.
i exists, and the output voltage vectors corresponding to each switching mode are six as shown in FIG. Here, vector (U
, V, W) indicate the state of the two transistors in each arm of U, V, and W of the inverter main circuit, "1" means the upper transistor is on and the lower transistor is off, and "0"
indicates that the lower transistor is on and the upper transistor is off. For example, the output voltage vector Vz(1,,1°0) is output when transistors Qu, Qv, Qz are on and transistors Qx, Qv, Qw are off.

Now, by sequentially switching such switching modes, the vector indicating the voltage phase of the motor can be considered to actually rotate around point O in FIG. 9. However, since the output 1u pressure vector that the inverter device can actually output is any one of the six discrete lines shown in Figure 9, a fixed phase voltage vector is output during DC braking. will be done.

(Problem to be Solved by the Invention) However, the point in time at which the DC braking command is given is uncertain. Therefore, depending on the time point at which the command is given, the actual voltage phase and the phase of the output voltage vector during DC braking may deviate by up to 360 m. This means that when transitioning from the operating state to DC braking, a transient torque is generated depending on the phase difference, resulting in large variations in braking torque and variations in the motor's stopping state. I will do it.

On the other hand, the switching mode for DC braking is
It is also conceivable to select the output voltage vector that is closest to the voltage phase at that time. However, as mentioned above, there are only six output voltage vectors at 60" intervals that the inverter can actually output, so even with this method, a deviation of up to ±30" will occur, causing transient torque during DC braking. It is inevitable that this will occur. With this, the stop position may be inaccurate in applications where the motor is controlled to rotate at low speed and a stop command is given based on the activation of a proximity switch, and the motor is stopped within a certain range from the activation position of the proximity switch. Therefore, it cannot be adopted at all.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an inverter device that can always maintain a stable stopping position of an electric motor when the electric motor is stopped by DC braking.

[Structure of the Invention] (Means for Solving the Problems) The inverter device of the present invention repeats two switching modes during DC braking so that the phase of the combined output voltage vector of the inverter main circuit is the same as the voltage phase at the start of DC braking. The feature is that they are made to be approximately equal.

(Function) Since the phase of the composite output voltage vector during DC braking is approximately equal to the voltage phase at the start of DC braking, generation of transient torque during DC braking can be suppressed.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

As shown in FIG. 2, the inverter main circuit 11 has a well-known configuration, with a converter section 13 rectifying alternating current from an alternating current power source 12, and an inverter section 14 converting the rectified alternating current into alternating current. The inverter section 14 includes a total of six transistors Qu+Qv, Qw, Qx, Qv, and Qz as a switching element group, and two of these transistors are allocated to each of three arms to form a three-phase configuration. This group of transistors is controlled on and off via a base amplifier 16 by a control circuit 15 equipped with a microcomputer.

In addition, in the transistor group with the above configuration, except for the IFIi type switching mode in which all transistors are turned off, the only meaningful switching modes are 6P! i exists, and the output voltage vectors corresponding to each switching mode are six as shown in FIG.

Here, for example, vector Vv (0, 1, O) has transistors Qx, Qv, Qz on, transistor Qu,
As in the prior art, it means the output voltage vector output when Qy and Qw are off. When the electric motor 17 is connected to the inverter main circuit 11 and 1 jl of AC power is supplied, the switching modes of the transistor groups are sequentially switched at predetermined timings, and as a result, the output voltage vector changes in the clockwise direction in FIG. will be output sequentially.

Now, the control circuit 15 is configured with a microcomputer of a well-known configuration consisting of a CPU, ROM, RAM, etc.
In addition to sequentially switching the switching mode of the transistor group so as to rotate the output voltage vector, the motor is configured to flow direct current through the windings of the motor 17 to perform direct current braking when a braking command Ss is given. A software jM configuration for this purpose is shown in FIG. 1, and the operation of the present invention will be described below based on this.

First, the ROM of the microcomputer stores switching tables corresponding to the six types of switching modes described above, as shown in the following table, and variables THI and TH2 are stored in a predetermined area of the RAM. This variable TH
I is a voltage vector corresponding to the voltage phase applied to the windings of the motor 17, which is A in FIG. -A, the variable TH2 takes a value of 0 to 5 indicating in which region it is located, and the variable TH2 takes a value of 0 to 239 indicating the angular position obtained by subdividing each region of the range 60@ into, for example, 240.

Now, when the braking command SO is given while the electric motor 17 is in operation, the DC braking routine shown in FIG. 1 is executed. Here, first, the variable THI is read from the ROM, and based on this, the output voltage vectors V, V2 are determined (step a). These output voltage vectors V, , V2 correspond to two output voltage vectors sandwiching the voltage vector Vstor corresponding to the voltage phase at the time when the braking command S is given from both sides, and the voltage vector V sr. , for example, as shown in FIG. 3, the output voltage vectors V, , V, become Vz and Vv, respectively. , after this, R
The variable TH2 is read from OM, and the values of m and n are calculated based on this. The values of nt and n represent the ratio of the output time of the output voltage vector V z +Vv to the ON time of DC braking, which is predetermined depending on the magnitude of the braking torque, etc., and are calculated as follows. Ru.

First, a composite vector V as shown in FIG. think of. Composite vector■. Since satisfies the following formula (1), the variable TH2
m shown in the same figure using . +n11 using the following formulas (2) and (3)
It can be approximated as follows.

V (1-m 0V 1 + no V 2
・・・・・・ (1)mo” (240
-TH2)/240- (2)no -TH
2/240 ・= −(3) However, this composite vector V. Since the magnitude of the vector changes slightly depending on the angle, we should consider the resultant vector {circle around (2)} as shown in FIG. When the fifth self is enlarged, it becomes as shown in FIG. 6, from which the following equation is established.

(m lV+ l +n IV2 1/2)'
+ (5n Iv2 1 /2) ” -IV
t I 2 (4) Here, since IV+ l −IV21, the above equation can be rewritten as follows.

rn2+n2+mnm1 ・・・・・・(5
) Also, since the composite vectors Vo and V have the same phase, tn/n - tn, /n. Therefore, regarding m and n, the following equations (6) and (7) hold true after all.

m=17(α2+α+1)""' --(6)n=1
/ (β2+β+l)1''2 ・・・・・・(7)
Here, amn, 7m.

β-mo/no.

After calculating the types of output voltage vectors V, , V and their output time ratios m and n in this way, the variable V l”A
Set TN to 2-bit data “10” (Step C)
. Then, in step d, the lower bit of the variable V,·,A, is tested, and if it is "0", the output voltage vector ■,
The switching mode is set to output the output voltage vector V, and if it is "l", the switching mode is set to output the output voltage vector V. In this case, when the axis is set to "10" for the variable VP8, first the output voltage vector v1 is output (step e), and then this is maintained at m- for a time (step f).

Note that here m is the value obtained by the calculation in step b, and t
is the ON time determined by the magnitude of the braking torque, etc. (This time is IV+I'' in Fig. 3.
IV2 I). Output voltage vector V, force (m
After being output for the time at, all the transistors' are turned off, which maintains T -m for the time (
Steps g, h). After this, the variable v7a is rotated by 1 bit to "01" in step l), and on the condition that the preset DC braking time has not elapsed, return to step d. This time, the output voltage vector It takes a switching mode that outputs v2. In this case, the on time of the output voltage vector v2 is low and the off time is Tm-. Thereafter, this is repeated until the DC braking time has elapsed, so that the output voltage vectors V, V2 are output alternately as shown in FIG. As a result, as is clear from FIG. 3, the composite output voltage vector V output during 2 loops (27 in time) has the same phase as the voltage vector at the start of DC braking. Therefore, no transient torque is generated when transitioning from the operating state to the braking state, and a stable braking force acts to stop the electric motor at the set position.

[Effects of the Invention] As described above, according to the present invention, the phase of the composite output voltage vector during DC braking is approximately equal to the voltage phase at the start of DC braking, so that transient torque is not generated during DC braking. This has the excellent effect of suppressing the amount of noise and ensuring that the motor stops at a stable position at all times.

[Brief Description of the Drawings] Figures 1 to 7 show an embodiment of the present invention, with Figure 1 being a flowchart of a DC braking routine, Figure 2 being an overall block diagram, and Figure 3 being an inverter main circuit. Vector diagram showing the output voltage vector of 1. 4 to 6 are vector diagrams for explaining the combined output voltage vector, and FIG. 7 is a diagram showing the output voltage vector during DC braking in time series. FIG. 8 is a circuit diagram showing the basic configuration of the inverter main circuit, and FIG. 9 is a vector diagram showing the output voltage vector. In the drawings, 11 is the inverter main circuit, 13 is the converter section, and 15 is the control circuit.

Claims (1)

[Claims] 1. Output alternating current to the electric motor so that the output voltage vector sequentially rotates by sequentially switching the switching modes in the switching element groups of the inverter main circuit, and also cause the switching element groups to perform predetermined switching when a braking command is given. mode, in which direct current is applied to the windings of the motor to perform direct current braking, and during direct current braking, two switching modes are repeated so that the phase of the combined output voltage vector of the inverter main circuit changes to the point at which direct current braking starts. An inverter device characterized in that the voltage phase is approximately equal to the voltage phase at the time.