JPH0311904A - Modulation of inverter - Google Patents

Abstract

PURPOSE:To reduce pulse width variations by the switching of modes between the 1st mode of 9 pulses and 2nd mode of 5 pulses and to prevent the sudden change of an inverter output by setting a designated transient mode for modulation between the above 1st and 2nd modes. CONSTITUTION:In switching from the 1st mode where nine pulses are distributed in the range of 180 deg. of output voltage 20 in variable voltage and variable frequency to the 2nd mode where five pulses are distributed in the range of 120 deg. thereof, each pulse width and pulse interval of a pair of output pulses 22 and 23 existing in each phase at 0 deg. and 180 deg. of the output voltage 20 in the 1st mode is reduced one after another, while a transient mode to reduce the zero output width in the phase of 60 deg. and 120 deg. of the output voltage 20 one after another eown to the designated minimum time width determined by the switching performance of a switching element is set between the 1st and 2nd modes. With the pulse width variations reduced, the sudden change of motor current and output torque can thereby be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of modulating an inverter such as a three-phase inverter that drives and controls an induction motor, for example.

[Conventional technology]

Figures 2 to 4 illustrate a conventional inverter modulation method of this kind, which is described in, for example, Paper 73 of the 1973 Federation of Electrical Engineers of Japan Conference ``On Inverter Control of Induction Motors for Vehicles (Part 2)''. FIG. 2 is a circuit diagram showing the main circuit configuration of the inverter, FIG. 3 is a block diagram showing the control circuit configuration thereof, and FIG. 4 is a time chart showing its operating waveforms.

In the figure, (1) is a DC power supply, ■ is a switch that turns on and off the main circuit, θ) and (2) are filter reactors and filter capacitors that constitute an inverted filter circuit, respectively, (5U) to (5Z) (6) is a semiconductor switch such as a thyristor as a switching element connected to a three-phase bridge and constitutes an inverter, (6) is an induction motor, (7)
is a current detector (8) that detects the current of the induction motor (6);
) is a pulse generator that detects the rotation frequency of the induction motor (6).

(9) is an operation command that is an input condition for control, 00) is a current command generation unit that generates a current command rp based on the command from operation command (9), and (11) is also a command from operation command (9). The frequency command generator (12) generates the slip frequency command fsp based on the output of the current command generator αO) and the signal of the current rM of the induction motor (6) detected by the current detector (2). (13) is a current control unit that calculates the output voltage V; (13) is a slip control unit that calculates the slip frequency fs of the induction motor (6) from the output of the frequency command generation unit (11) and the current IM signal; (14) is a slip control unit that calculates the slip frequency fs of the induction motor (6); The output frequency F of the inverter is calculated from the rotation frequency fM from the pulse generator (a) and the slip frequency fs from the slip control unit (13).
The adder (15) is a modulation circuit that sends a gate signal to each semiconductor switch (5U), etc. with the output voltage (2) and output frequency (F) as the target.

Next, the operation will be explained. The current command 1p generated by the current command generation unit 00) based on the command from the operation command (9) is compared and amplified with the current signal IM in the current control unit (12), and the output of the inverter to be applied to the induction motor (6) is The voltage becomes the voltage ■ and is input to the modulation circuit (15). In addition, driving commands (
The slip frequency command fsp generated by the frequency command generator (11) in accordance with the command from 9) is compared and amplified with the current signal IM in the slip control unit (13), and is added as the slip frequency fs of the induction motor (6). The signal is input to the device (14). The adder (14) combines this slip frequency fs and the pulse generator (
8 and the rotational frequency fM from 8 are input, and according to the following formula, the output frequency F of the inverter is sent to the modulation circuit (15) by adding when accelerating the induction motor fi [61 and subtracting when regenerating.

F=fM:th:fs (1)
Based on the commanded output frequency F and output voltage ■, the modulation circuit (15) generates a sinusoidal U-phase modulated wave (16) and a triangular carrier wave (17) according to a predetermined mode, for example, as shown in FIG. Set as shown.

Then, the waveforms of the U-phase modulated wave (16) and the carrier wave (17) are compared to obtain a U-phase modulated signal (18) that is inverted at the intersection. The on/off timing of the semiconductor switches (5U) and (5X) shown in FIG. 2 is determined according to the output level of this U-phase modulation signal (18).

Similarly, a phase modulation signal (19) is obtained from a carrier wave (17) and a V phase modulation wave (not shown) delayed by 120° from the U phase, and the semiconductor switch is switched according to the output level of this V phase modulation signal (19). Determine the on/off timing of (5V) and (5Y). For example, a UV phase-to-phase output voltage (20) is obtained as the output voltage of the inverter from the firing operation of the semiconductor switch based on the U-phase modulation signal (18) and the -phase modulation signal (19).

By the way, the acceleration of the induction motor (6) progresses and the output frequency F
As the voltage increases, it is necessary to increase the switching frequency of the semiconductor switches that constitute the inverter accordingly. However, semiconductor switches have an upper limit to their switching frequency due to their switching performance and usage conditions, and for this reason, as the output frequency F increases, the number of output pulses included in the inverter's output voltage waveform increases stepwise. For example, the method of reducing
AC motor drive/inverter control system for electric vehicles” 2.3
8 to 39 introduce a method of switching the output pulse in each mode of asynchronous → 21 pulses → 15 pulses → 9 pulses → 5 pulses → 3 pulses → 1 pulse.

Figure 5 shows each waveform when switching from the 9 pulse mode to the 5 pulse mode among the above pulse mode switching. The waveform is changing. That is, the waveform of the UV phase-to-phase output voltage (20) up to time A is in the first mode with 9 pulses distributed over a 180° range during its half cycle, and the UV phase-to-phase output voltage (20) after time A is
The waveform is in the second mode in which five pulses are distributed over the 120° range, and at this point A, the first mode is switched to the second mode.

Note that (21) in FIG. 5 is a sinusoidal V-phase modulated wave.

[Problem to be solved by the invention]

In the conventional inverter modulation method, as described above, 18
From the first mode with 9 pulses distributed in the 0° range,
Direct switching to the second mode in which 5 pulses are distributed over a 120° range causes large pulse width fluctuations, causing sudden changes in the current and output torque of the induction motor (6), resulting in poor riding comfort, etc. was there.

This invention was made to solve the above-mentioned problems. In particular, it smoothly switches the modulation mode between 9 pulses and 5 pulses, reduces pulse width fluctuations, and reduces sudden changes in motor current and output torque. The purpose of this invention is to obtain an inverter modulation method that can prevent this.

[Means and effects for solving the problem] In the inverter modulation method according to the present invention, the following transient mode is set between the first mode and the second mode.

That is, 0° and 18° of the output voltage in the first mode.
The pulse width and pulse interval of the pair of output pulses present in each of the 0° phases are sequentially reduced, and the 0 output width at the 60° and 120° phases of the output voltage in the first mode is reduced by the switching element. The time width is gradually reduced to a predetermined minimum time width determined from the switching performance.

After this transient mode is completed, switch to the second mode. When returning from the second mode to the first mode, the operations described above are performed in the reverse order.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows each waveform in this embodiment corresponding to the conventional figure 5, and in the figure, each waveform is given the same reference numeral as in the conventional figure. In the figure, before time A, the first of nine pulses
In this mode, the operation is the same as the conventional operation before time A in FIG. 5. After time 0 B, there is a second mode of 5 pulses, which is the same operation as the conventional operation after time A in FIG. However, compared to the conventional case, the UV phase-to-phase output voltage (20) starts from a phase shifted by half a cycle. The part from point A to point B is the transient mode that we inserted this time.
In order to simplify the illustration, in FIG. 1, the period ends in a half cycle, but in reality it takes a longer period and changes gradually.

Next, the specific operation of the modulation circuit (15) in this transient mode will be explained with reference to FIG. Output frequency F is 9
When the upper limit value of the pulse mode is reached (time A), the modulation circuit (15) detects this and shifts to the transient mode.
The waveform of the carrier wave (17) is sequentially deformed, that is, the UV
Phases of phase-to-phase output voltage (20) 0°, 60°, ! 20'
, 180° (0”), ... carrier wave (17)
Gradually lower the peak position of the triangular wave, however, as shown in the figure, leave the part with a predetermined minimum time width ΔT determined from the switching performance of the semiconductor switch (5U), etc., and lower the peak position of the triangular wave. .

At the same time, the phase 60 of the transient mode gradually widens the time width TW between the apex and the two adjacent apexes with opposite polarity.
The triangular waveform partially indicated by a dotted line at the angle is the waveform of the carrier wave (17) in the 9-pulse mode for reference.

Due to the above waveform repetition of the carrier wave (17), the zero output width at phases 60° and 120° of the UV phase-to-phase output voltage (20) gradually decreases and eventually reaches the minimum time width ΔT (indicated by C in the figure). Also, the phase 0 of the UV phase-to-phase output voltage (20)
Originally, in the 9-pulse mode, a pair of output pulses (22) and (23) exist in the 180° and 180° portions, but by operating the lower carrier wave (17), these output pulses (22) ( 23), each pulse width and pulse interval gradually decrease and eventually disappear (indicated by circles in the figure).

Then, the peak position of the carrier wave (17) reaches the zero level,
The transient mode ends when the time width TW matches that of the 5-pulse mode, and then the mode shifts to the 5-pulse mode. On the other hand, when switching from 5-pulse mode to 9-pulse mode, the above operation may be performed in reverse.

By appropriately setting the number of cycles of this transient mode,
Switching between the 9-pulse first mode and the 5-pulse second mode can be performed continuously and smoothly, and sudden changes in motor current and output torque can be prevented.

In addition, the operation of the waveform of the carrier wave (17) explained above is as follows.
For example, necessary waveform data may be stored in a ROM built into the modulation circuit (15) and retrieved as needed.

Further, in the above embodiment, the U-phase modulated wave (16) is a sine wave, but it may be a square wave, and the carrier wave (17) is not limited to a triangular wave, but may be a wave such as that described in JP-A-58-179176. Various waveforms may be employed.

〔Effect of the invention〕

As described above, in this invention, a predetermined transient mode is set and modulated between the first mode of 9 pulses and the second mode of 5 pulses, so that the first mode and the second mode are Pulse width fluctuations due to mode switching are reduced, and sudden changes in the inverter output are prevented.

[Brief explanation of the drawing]

FIG. 1 is a time chart of each waveform to explain the modulation operation according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the main circuit configuration of the inverter, and FIG. 3 is a block diagram showing the control circuit configuration. , the fourth section is a time chart for explaining the basic operation, and FIG. 5 is a time chart for explaining the conventional modulation operation. In the figure, (5U) to (5z) are semiconductor switches as switching elements, (15) is a modulation circuit, and (16)
is the U phase modulated wave, (17) is the carrier wave, (20) is the UV phase-to-phase output voltage, (21) is the ■ phase modulated wave, (22) (23)
is the pair of output pulses, and ΔT is the minimum time width. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] An inverter that sets a modulated wave and a carrier wave in a predetermined mode and controls on/off switching elements of the inverter using a gate signal obtained by comparing the two waves to obtain an output voltage of variable voltage and variable frequency. In the modulation method of the above, when switching from a first mode in which 9 pulses are distributed in a range of 180° of the output voltage to a second mode in which 5 pulses are distributed in a range of 120° of the output voltage, 0° and 180° of output voltage in the first mode
While sequentially reducing each pulse width and pulse interval of a pair of output pulses existing in each of the phases of °,
A transient mode in which the zero output width at the 60° and 120° phases of the output voltage in the mode is sequentially reduced to a predetermined minimum time width determined from the switching performance of the switching element is divided into the first mode and the second mode. An inverter modulation method characterized by setting between