JP3206218B2 - Instantaneous value control method of voltage type inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instantaneous value control method for a voltage type inverter in which a switching frequency is constant without depending on a phase of a sine wave command voltage.

[0002]

2. Description of the Related Art FIG. 4 shows a circuit configuration of a motor driving inverter. In order for the inverter 1 to drive the motor IM smoothly, it is desirable that the load current be a sine wave. For this reason, a constant hysteresis width instantaneous value control method as shown in FIG. 4 is frequently used.

In this method, a sine wave command current i * (= Isi
nθ) and the load current i detected by the current detector CT are compared by a comparator 9 having a constant hysteresis width Δi.
When i−i * │> Δi, ON / OFF of the semiconductor switches S1 and S2 of the upper and lower arms of the inverter is inverted, and the polarity of di / dt is inverted. This control is performed independently for each of the U, V, and W phases. FIG. 5 shows an example of this operation.

[0004]

The above-mentioned conventional control method is as follows.
Since the hysteresis width Δi of the comparator 9 is constant, the switching frequency of the semiconductor switches S1 and S2 decreases near θ ≒ 0 ° at the command current i * = Isin θ,
It becomes high near θ = 90 ° (FIG. 5). That is, in the conventional instantaneous value control method, the switching frequency differs depending on the phase of the command current.

When the switching frequency of a motor driving inverter exceeds a certain value (或 20 KHz), noise exceeds the audible range and becomes inaudible to humans. But θ =
Since the switching frequency is low near 0 °, noise is generated due to this frequency component.

If the hysteresis width Δi is reduced, θ =
Although the switching frequency near 0 ° can be set to be higher than the audible range, the average switching frequency of the inverter also increases, the switching loss increases, and the efficiency of the inverter decreases.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and an object of the present invention is to make the switching frequency of the inverter higher than the audible range without lowering the efficiency of the inverter. It is an object of the present invention to provide a possible instantaneous value control method of a voltage source inverter.

[0008]

In order to achieve the above object, an instantaneous value control method for a voltage source inverter according to the present invention detects a difference between a sine wave command current and an output detection current,
The absolute value of the difference current as compared to the hysteresis width, when the absolute value is larger than the hysteresis width, inverter
ON the semiconductor switch of the upper lower arm, the voltage source inverter for inverting the OFF, the hysteresis width,
With a variable hysteresis width that varies the phase of the command current of the sine wave, is almost constant becomes and the switching frequency does not depend on prior <br/> Symbol switching frequency of the command current of the semiconductor switch phase the variable hysteresis width This is set so as to be larger than the audible region.

[0009]

When the hysteresis width is constant, the switching frequency of the inverter is set to 90 ° for the phase of the sine wave command current and 2
It increases near 70 ° and decreases near 0 ° and 180 °, but the hysteresis width is a variable hysteresis width that changes according to the phase of the sine wave command current, so the switching frequency is kept constant regardless of the phase of the command current. be able to.

[0010] It is difficult to the switching frequency audible range or in the hysteresis width constant when the total phase, and the switching frequency is constant regardless of the phase, the audible region above without increasing the average switching frequency It is possible to

[0011]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a motor driving inverter and a control circuit for one phase of the inverter. In the figure, reference numeral 1 denotes an inverter including semiconductor switches S1 to S6, and IM denotes an inverter 1.
The motor driven by CT is a U-phase output (load) current detector.

2 to 7 are upper and lower U-phase semiconductor switches S
1, a U-phase control circuit for controlling S2, 2 is a current detector C
A current difference detector 3 for calculating a difference between a detected current i from T and a command current i * (= Isin θ), and an absolute value converter 3 for obtaining an absolute value of an output ii * of the current difference detector 2.

4 is the input of the command current i * = Isin θ,
Due to the amplitude I and the phase θ, the hysteresis width Δi becomes narrow near θ = 0 ° and 180 ° and widens near θ = 90 ° and 270 ° as shown in FIG. A variable hysteresis width calculator for calculating a variable hysteresis width Δi ′ that can be constant without depending on the phase θ of the command current i * as shown in FIG. 2B.

Reference numeral 5 denotes a comparator for comparing the output (i−i *) of the absolute value converter 3 with the output Δi ′ of the arithmetic unit 4 (FIG. 3A), and 6 denotes a pulse from the comparator 5 (FIG.
Flip-flop (b)) is input to the CLK terminal, 7
Reference numeral denotes a dead time generation unit that applies a dead time to the S1 on signal output and the S2 on signal output (FIG. 3C) of the flip-flop to output the semiconductor switch S1 gate signal and the S2 gate signal. The semiconductor switches S3, S4 and S5, S6 are similarly controlled.

With the above configuration, the variable hysteresis operation section 4 outputs a variable hysteresis width Δi ′ such that the switching frequency becomes constant from the command current i *. Thus, the output from the absolute value converter 3 is:
* ·> Δi 'when it comes to being outputted from the comparator 5 to the CLK terminal of flip-flop 6 for inverting the output of the flip-off drop. Therefore, the on / off states of the gate signals of the semiconductor switches S1 and S2 are inverted, and again, * ii ** <
Δi.

Therefore, | i−i * | ≦
Δi is maintained, and the output current i is controlled as shown in FIG. Accordingly, since the ON periods of the semiconductor switches S1 and S2 are uniform as shown in FIG. 2B, it is possible to increase the audible frequency or higher without changing the average switching frequency.

[0017]

Since the present invention is configured as described above, the following effects can be obtained.

(1) The switching frequency of the semiconductor switch of the inverter can be made substantially constant.

(2) The switching frequency in all phases of the command current can be set higher than the audible range without increasing the average switching frequency of the inverter.

(3) Therefore, the noise generated from the inverter can be suppressed without increasing the loss of the inverter.

(4) Since the switching frequency is substantially constant, the time width of the dead time can be easily set.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram of an inverter according to an embodiment of the present invention.

FIG. 2 is a waveform chart illustrating a control method according to the embodiment.

FIG. 3 is a diagram illustrating the operation principle of a control circuit according to an embodiment.

FIG. 4 is a control circuit diagram of an inverter according to a conventional example.

FIG. 5 is a waveform diagram illustrating a control method according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inverter 2 ... Difference detector 3 ... Absolute value conversion part 4 ... Variable hysteresis width calculation part 5 ... Comparator 6 ... Flip-flop 7 ... Dead time generation part 9 ... Hysteresis comparator IM ... Motor S1-S6 ... Semiconductor switch

Claims (1)

(57) [Claims] 1. A method for detecting a difference between a sine wave command current and an output detection current, comparing an absolute value of the difference current with a hysteresis width, and when the absolute value is larger than the hysteresis width,
Semiconductor switch of ON of the lower arm on the inverter, OFF
In the voltage source inverter for inverting the dependence of the hysteresis width, with a variable hysteresis width that varies the phase of the command current of the sine wave, the phase of the switching frequency command current before Symbol semiconductor switches its variable hysteresis width The instantaneous value control method for a voltage-type inverter, wherein the switching frequency is set to be substantially constant and the switching frequency is higher than the audible range.