JPH0365060A - Three-phase inverter - Google Patents

Abstract

PURPOSE:To suppress higher order harmonics and avoid radio interference end misoperation of peripheral electronic apparatuses such as an earth leakage breaker by a method wherein respective waveforms are outputted from output terminals U, V and W in accordance with respective specific waveform formulae and voltages between respective phases are so controlled as to have sinusoidal waveforms. CONSTITUTION:Following output waveform data are inputted to a ROM waveform data part. That is, the data that a voltage expressed by a formula I is outputted to the U-phase for a reference voltage, the data that a voltage expressed by a formula II is outputted to the V-phase for a reference voltage and the data that a voltage expressed by a formula III is outputted to the W-phase for a reference voltage are respectively inputted. A voltage control circuit 37 contains a comparator and compares the AC voltage waveforms outputted from respective output terminals U, V and W with the waveforms outputted from a multiplying circuit 36 to correct the AC voltage waveforms outputted from the output terminals U, V and W. With this constitution, sinusoidal waveform output voltages can be obtained and higher harmonics can be suppressed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a three-phase inverter device that converts AC power into a predetermined frequency and voltage and outputs the same, and in particular relates to an ultra-precision inverter device that requires smoothness and stability. The present invention relates to a three-phase inverter device suitable for controlling drive motors for machine tools.

<Prior Art> Recently, with the advancement of mechatronics, the demand for induction motors capable of speed control is increasing.

In order to drive this type of induction motor, it is known to use a converter called an inverter that converts an AC power source to a predetermined frequency.

Conventionally, the following two methods of controlling output voltage using an inverter are known.

One of them is PWM (pulse width mo
An example of the voltage waveform is shown in FIG.

This PWM control method is a method of adjusting pulse width and frequency by controlling on/off of transistors.

The other is PAM (pulse ai+pulitu
FIG. 9 shows an example of the voltage waveform using the de modula-tion) control method.

This PAMi control method is a method of adjusting the voltage and frequency of a rectangular wave.

<Problems to be Solved by the Present Invention> The conventional three-phase inverter devices described above have the following common problems.

<B> Both control methods include high-order harmonics in their respective output voltages.

This causes radio wave interference and malfunction of peripheral electronic equipment, such as industrial robots, NC control panels, and earth leakage circuit breakers.

<Mouth> Since it outputs a square wave, the power supply to the induction motor is continuously on and off.

As a result, the iron core vibrates, causing the induction motor to vibrate and produce abnormal noise.

<C> Since both control systems use square waves, the smoothness of rotation varies depending on the rotation speed of the induction motor.

In particular, the slower the induction motor rotates, the less smooth the rotation tends to be.

Therefore, it is desired to propose an inverter that can smoothly control the rotation of an induction motor at both low and high speeds.

<2> When the input line voltage As1nω+t [V] is rectified, the DC output voltage becomes A [V].

Suppose that the voltages of the U phase, ■ phase, and W phase are respectively Es1n(ωt) [V] Es1n(cc>t −2π/3) [V] Es1n(
When ωt+2z/3)[V], the maximum amplitude from the negative voltage to the positive voltage is 2E.

If this is created from DC voltage, E=A/2.

The phase-to-phase voltage on the output side of the conventional inverter that will be created from now on is J3 Es1n (ωt+π/6) [V] J3 Es1
n(ωt −z/2) [V]J3 Es1n(ωt+
5z/6) [V], and -r372 of the input voltage
You can only get double the voltage.

A possible solution to this problem is to boost the input voltage by 27f3 times using a transformer and then rectify it.

However, this method has the drawback of being expensive and is therefore not very practical.

In the above formula, ωI is the angular velocity of the input voltage, ω is the angular velocity of the output voltage, t is time, A is the voltage constant on the input side, and E is the voltage constant on the output side.

<Objective of the present invention> The present invention has been developed to solve the above-mentioned problems, and its objects are as follows: (a) To prevent the generation of high-order harmonics and to prevent radio interference and earth leakage. (b) Prevents the induction motor from generating vibrations and abnormal noises; (C) Furthermore, the rotation of the induction motor is smooth from low speed to high speed. The purpose of the present invention is to provide a three-phase inverter device.

<Means for solving the problem> That is, the present invention comprises a rectifier circuit that rectifies an AC power source into a DC voltage, an output circuit connected to the output side of the rectifier circuit, and a control section that controls the output circuit. , the control unit outputs waveforms from the output terminals U, V, and W of the output circuit based on the following waveforms, and each phase-to-phase voltage output from the output terminals U, V, and W is configured to be a sine wave. This is a three-phase inverter device.

When the reference voltage is negative, U phase: Vu=Esin(ωt)+E/6sin(3ωt)-1 with respect to the reference voltage
-v73E/2V phase: Vv=Esin(ωt-2π/3)+E/6sin(3
ωt) + aE/2W phase: Vw=Esin(ωt +2z/3) +E/6sin with respect to the reference voltage
(3ωt) + aE/2 Furthermore, Vu is the output voltage relative to the U-phase reference voltage, Vv is the output voltage relative to the V-phase reference voltage, Vw is the output voltage relative to the W-phase reference voltage, ω is the angular velocity, t is the time, E is a voltage constant.

<Description of the present invention> The present invention will be described below with reference to the drawings.

<A> Overall structure of the device FIG. 1 shows an example of a control circuit diagram of an inverter device according to the present invention.

To explain the control circuit of the inverter device, 10 is a rectifier circuit made of a diode, 20 is an output circuit connected to the output side of the rectifier circuit 10, and 30 is a control section connected to the output circuit 20.

The rectifier circuit 10 includes a smoothing circuit, and has an input terminal, RlS, T
It is connected to the three-phase power supply supplied by the electric power company via the

The output circuit 20 controls the DC voltage rectified by the rectifier circuit 10, and is made of, for example, a known FET (field effect transistor) or transistor, and has output terminals U, V, and W.
It is connected to an induction motor (not shown) via.

The control section 30 includes an input circuit 31, a V/F conversion section 32, a counter 33, a ROM waveform data 2 section 34, and a D/A conversion section 35.
The multiplication circuit consists of an arithmetic circuit 36 and a voltage control circuit 37.

The V/F conversion unit 32 is a known unit that converts the voltage of the speed command output from the input circuit 31 into a frequency.

The counter 33 is for changing the address of the ROM waveform data 2 section 34.

The ROM waveform data 2 section 34 stores output waveform data of each phase as described later.

The D/A converter 35 converts the digital signal extracted from the ROM waveform data 2 section 34 by address operation of the counter 33 into an analog signal.

The multiplication circuit 36 is a circuit that adjusts the fixed waveform output by the D/A converter 35 to a voltage based on the speed command.

The voltage control circuit 37 includes a comparison circuit, and compares the AC voltage waveform output from each output terminal U, V, W of the output circuit 20 and the waveform output from the multiplication circuit 36,
This is a circuit for modifying the AC voltage waveform output from output terminals U, V, and W.

It goes without saying that the inverter section constituted by the output circuit 20 and the control section 30 includes a converting means for converting the DC voltage rectified by the rectifier circuit 10 into an AC voltage.

<Explanation> Waveform data The inverter device of the present invention uses two parts of ROM waveform data in order to prevent the generation of high-order harmonics and bring the interphase voltage waveform finally output from the output terminals ty, v, and w closer to a sine wave. 34, input the next output waveform data.

Note that the output waveform data below shows the case where the reference voltage is set to the negative side as shown in FIG.

[U phase 1 As shown in the output waveform in Fig. 3, the U phase is Vu = Esin (ωt) + E/6 sin (3ωt) +
Input data to output a voltage of 4E/2.

[For the V phase J (2) phase, as shown in the output waveform in Fig. 4, Vv =Esin(ωt-2z/3)+E/6sin(
Input data to output a voltage of 3ωt) + 4E/2.

[W phase] The W phase is Vw=Esin(ωt +2z/3) +E/6sin with respect to the reference voltage as shown in the output waveform in Figure 5.
Input data to output a voltage of (3ωt)+3E/2.

That is, as shown in FIG. 6, the phase-to-phase voltage between each phase is calculated by the following equation.

Phase-to-phase voltage Vu-Vv=J3Esin(ωt+π/6)
[V] Phase-to-phase voltage Vv-Vw = aEsin(ωt-π
/2) [V] Phase-to-phase voltage Vw-Vu=4Esin(ωt
+5z/6) [V] Therefore, the output waveforms of each phase are sinusoidal voltages that are shifted by 1/3 period (2π/3 radians) from each other.

In other words, in the present invention, the voltage of each phase is E/6sin(3ωt
), the maximum value of the voltage amplitude becomes /3E.

If this is created from a DC voltage, the voltage constant (E) is A/, /:
becomes.

The voltage between each phase created from this is J3 Es1n(ωt+z/6) [V]-13Es1
n (ω to -/2) [V] J3 Es1n (ωt+5
π/6) [V], and a voltage that is one time that of the input terminal can be obtained without boosting the voltage using a transformer as in the conventional case.

In the above output wave format, Vu is the output voltage relative to the U-phase reference voltage, Vv is the output voltage relative to the V-phase reference voltage, and V-
is the output voltage with respect to the W-phase reference voltage, ω is the angular velocity, t is time, and E is the voltage constant.

<Action of the present invention> Next, the operation of the inverter device will be explained.

In FIG. 1, a three-phase input power source is manually input to a rectifier circuit 10 and rectified into a DC voltage.

The rectified DC voltage is input to the output circuit 20.

On the other hand, in the control section 30, when a speed command for the induction motor is inputted to the input circuit 31 through a computer or manual operation, the V/F conversion section 32 first converts the output voltage of the input circuit 31 into a frequency.

Subsequently, the counter 33 changes the address of the ROM waveform data 5 part 34 based on the input command converted into a frequency, so that the ROM waveform data 5 part 34 changes based on the waveform data input to the ROM described above. Each fixed basic waveform of each U phase, ■ phase, and W phase as shown in FIGS. 3 to 5 is output.

Furthermore, the basic waveform of each phase is converted from a digital signal to an analog signal by a D/A converter 35.

Since each output waveform output from the ROM waveform data section 34 has a fixed shape, it is necessary to adjust the voltage to a voltage based on the speed command.

This voltage adjustment is performed by the multiplication circuit 36.

The multiplication circuit 36 multiplies the voltage waveform output by the D/A converter 35 by the voltage immediately before being input to the V/F converter 32, and outputs the voltage waveform adjusted based on the input command to the voltage control circuit. 37.

The voltage control circuit 37 compares this with the divided voltages of U, V, and W, and when the voltages of U, V, and W are high, turns on the FET or transistor to lower the voltage, and vice versa. When the voltages of U, V, and W are low, a signal is sent to the output circuit 20 to turn on the FET or transistor in order to increase the voltage.

The output circuit 20 outputs waveforms adjusted based on the rotation command from output terminals U, V, and W, respectively.

In addition, the output waveform of each phase from the output circuit 20 is sent to the voltage control circuit 3.
7. Feed back to correct the output voltage.

Incidentally, when the reference voltage is determined on the positive side as shown in FIG. 7, it goes without saying that the DC voltage J3E/2 added to Vu, Vv, and V- may be set on the negative side.

In this case, the output waveforms of each phase outputted from the output terminals U, V, and W have opposite poles of the waveforms shown in FIGS. 3 to 6.

<Effects of the Present Invention> As explained above, the present invention enables the output voltage to be an ideal sine wave without using a rectangular wave like the conventional PWM control method or PAM control method. Effects can be obtained.

<B> Since the generation of high-order harmonics can be prevented, there is no problem of radio wave interference or malfunction of peripheral electronic equipment.

<Mouth> Since the output voltage is a sine wave, the vibration and noise of the induction motor can be reduced.

<C> Regardless of the rotation speed, smooth rotation can be obtained from low speed range to high speed range.

<2> As in the present invention, E/6sin (
By adding 3ωt), a voltage that is one time the input voltage can be obtained without boosting the voltage using a transformer as in the conventional case.

<E> Malfunction of the earth leakage circuit breaker can be prevented.

Figure 9: An explanatory diagram of the conventional technology, which is an output waveform diagram using the PAM control method.

[Brief explanation of drawings]

Fig. 1: Control circuit diagram of the inverter device according to the present invention Fig. 2: Explanatory diagram when the reference voltage is set to the negative side Figs. 3 to 5: Output waveform diagram of each phase Fig. 6: Output from the inverter device Figure 7: An explanatory diagram when the reference voltage is set to the positive side Figure 8: An explanatory diagram of the prior art, which is an output waveform diagram using the PWM control method

Claims (1)

[Claims] (1) Consisting of a rectifier circuit that rectifies an AC power supply to a DC voltage, an output circuit connected to the output side of the rectifier circuit, and a control section that controls the output circuit, the control section Output terminals U, V, W of the output circuit
A three-phase inverter device configured to output a waveform from each of the terminals U, V, and W, and to output a sine wave between the phases from the output terminals U, V, and W. When the reference voltage is negative, U phase: Vu=Esin(ωt)+E/6sin(3ωt)+√ with respect to the reference voltage
3E/2V phase: Vv=Esin(ωt
-2π/3)+E/6sin(3ωt)+√3E/2W
Phase: Vw=Esin(ωt+2π/3)+E/6sin(3
ωt)+√3E/2Vu is the output voltage relative to the U-phase reference voltage Vv is the output voltage relative to the V-phase reference voltage Vw is the output voltage relative to the W-phase reference voltage ω is the angular velocity t is the time E is the voltage constant