JPS62181674A - Pulse width modulation type inverter apparatus - Google Patents

Abstract

PURPOSE:To drive a motor smoothly without damaging torque characteristics by correcting an output from a reference voltage generator for controlling an inverter output-voltage waveform so as to eliminate the effect of a period for preventing a short circuit in response to the load factor of an inverter. CONSTITUTION:A first reference wave generator 30 receives an output-frequency f0 command and an output-voltage V0 command, and generates a sinusoidal first reference waveform, and a second reference waveform generator 40 receives the f0 command and an fc information from a carrier pattern generator 90, and generates a rectangular wave-shaped second reference waveform. A synthesizer 60 receives the information of the power-factor angle phi of a power-factor detector 50, synthesizes outputs from the first and second reference waveform generators 30, 40, and outputs a reference waveform corresponding to three phase to a PWM signal generator 70. Accordingly, a motor can smoothly be driven stably without damaging output torque characteristics.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a pulse width modulation type inverter device that converts direct current or alternating current into alternating current of variable frequency and variable voltage by converting direct current using a forward converter. be.

[Conventional technology]

Figures 5 and 6 show, for example, the conventional pulse width modulation type inverter device shown in 1981 (T1 IEEJ Tokai Branch Union Conference 151rPWM Inverter's Upper and Lower Arm Short-Circuit Prevention Periods on the Effects on Waveforms). In the characteristic diagram, Vdc is 7J
10 is the main circuit section (inverse converter section) of an inverter device that converts the DC power supply Vdc into alternating current with variable frequency and variable pressure; 20 is the main circuit section; 10 is an electric motor driven by an induction motor, and 30 is an output frequency command (hereinafter referred to as FO command).
and a first reference waveform generator that receives an output voltage waveform (hereinafter referred to as Vo command) and outputs a base Q voltage waveform signal of each phase of the inverter; 70 is the first reference waveform generator 30;
Pulse width modulation (hereinafter referred to as PW) determines the switching pattern of the controllable element by comparing the gear signal with
A signal generator 80 (referred to as M) is a drive circuit that receives signals from the signal generation circuit 70 and drives the controllable elements. 9
0 is a carrier pattern generator that outputs a carrier waveform of a carrier frequency corresponding to the fo command. 100 is a V/f pattern generator that receives an fO command and outputs a VO command.

Next, the operation will be explained. First, FIG. 6 shows the PWM operation of one phase (U phase) of the three AC phases. The first reference waveform generator 30 receives the fo command.

When the Vo command is received, the proximal vaginal pressure waveform Vo as shown in FIG. 6(a) is output. The PWM signal generator 70 determines a switching pattern by comparing the carrier signal Vc and the reference waveform Vo as shown in FIG. 6(a).

FIG. 6(b) shows the switching patterns of the upper and lower subdivision elements (for example, transistors) of the U phase, TuP, 'f'UN (main circuit section 10 in FIG. 5), UFO, and UNO. The section where the reference voltage VO is greater than the carrier Vc is O.
N, the UFO is determined as OFF in the small section, and the reverse signal is set as [JNO]. The other V and W phases are similarly determined by comparing the same carrier with a reference voltage waveform whose phase is shifted by 1200 or 2400.

The on-off pattern is obtained as described above, and the on-off signals UP and UN output to the drive circuit 80 (Fig. 6 (
e)) is a so-called system in which a period in which both the upper and lower elements are turned off for a short-circuit prevention period Td is provided in order to prevent a short circuit between the upper and lower elements of the U phase due to a switching delay of the controllable element.
It is treated to prevent short circuits. Td is the normal drive circuit,
It is set sufficiently large to account for delays in controllable elements.

The same applies to the (2) phase and W phase signals. The drive circuit 80 receives on/off signals (Up, U) from the PWM signal generator 70.
N, etc.) to drive the controllable element. As a result, the inverter is in an operating state of frequency fo+voltage Vo.

For simplicity of explanation, drive circuit 80. Ignoring the delay in the controllable element main circuit section 10, the short circuit prevention period Ta2 is an uncontrolled period in which both the upper and lower controllable elements are turned off, so the potential of the output terminal depends on the polarity of the output current. It is determined by the function of the freewheeling diode. That is, in the case of a positive output current, the potential is negative, and in the case of a negative output a current, the potential is positive. This situation is shown in FIGS. 7(a) and 7(b).

The diagram shows the potential of the U phase with respect to the virtual neutral point of the inverter input.

Therefore, for example, the U-phase output voltage waveform does not become an ideal sine wave according to the on-off pattern tJpo, UNO,
It will have distortion. This situation is shown in FIGS. 6(d) and (e). (e) shows how the effect of the short-circuit prevention period Td mentioned above appears according to the output current polarity. If taken on average, it can be seen as a rectangular voltage waveform of -fo. The output voltage shown in (d) is Pw
' It is a combination of the ideal sine wave determined from the M signal UFO1UNO and the voltage affected by Td shown in (e).

If this situation is expressed in terms of the output line voltage and expressed by the following equation, it will be as shown in equation (1).

Here, TOv: U-V line voltage *Vdc: Inverter DC section voltage, A, B: Voltage output coefficient, φ: Power factor angle.

Td: Short circuit prevention period, Tc: PWM carrier period. In equation (1), the first term represents the voltage component that was originally intended to be controlled, and the second term represents the voltage component due to the influence of the short-circuit prevention period Td.

Further, since Td is generally fixed and Vdc is constant in this example, the amplitude of the second term is proportional to the five buttons.

The influence of the short-circuit prevention period Td is summarized as follows.

(1) Since the inverter output voltage does not become an ideal sine wave, the torque ripple and rotational ripple of the motor increase, resulting in increased vibration.

(2) As the load increases, the power factor becomes better (medium → small) (
1) The output voltage decreases because the phases of the first and second terms of the equation become closer. As a result, the output torque characteristics deteriorate.

(3) The electric motor cannot be driven stably.

Assuming that Tc is constant, these effects are more pronounced as Td is larger, and are more pronounced in the low frequency region where the output voltage level is low.

[Problem that the invention seeks to solve]

Since the conventional pulse width modulation type inverter device is configured as described above, its output voltage waveform does not become an ideal sine wave, and the influence of the short circuit prevention period Td appears according to the output current polarity, resulting in a distorted waveform. .

As a result, there were problems such as an increase in motor torque ripple and rotational ripple, a decrease in output torque, and an inability to stably drive the IE i machine, especially in the low frequency range where the output voltage is low.

This invention was made in order to solve the above-mentioned problems, and it uses pulse width modulation that can smoothly and stably drive the electric motor without impairing the output torque characteristics even in the low frequency range where the output t3 pressure is low. The purpose is to obtain a type inverter device.

[Pause: A precautionary measure to solve the problem]

The pulse IA modulation type inverter device according to the present invention includes:
In addition to the first reference waveform generator for output '1 and positive waveform control, a second reference waveform generator for output voltage waveform correction and a power factor detector for the inverter load are provided.

[For production]

In the PWM circuit according to the present invention, a power factor angle is detected from a power factor detector of an inverter load, and when the power factor is detected, the first reference waveform generator and the The output waveforms of the second reference waveform generator and the second reference waveform generator are combined to create a PwM signal.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as in FIG. 5 are denoted by the same reference numerals. In FIG. The reference waveform generator 50 detects the inverter output current, routes the power factor information to the power factor storage circuit, and detects the load power factor based on the original information, the power factor detector 60
is a synthesizer that receives power factor information from the power factor detector 50 and synthesizes the output of the first reference waveform generator 30 and the output of the second reference waveform generator 40 by shifting them by a power factor angle. 90 receives the fo command and sends a carrier pattern at a carrier frequency fc corresponding to fo to the PWM signal generator 70, and also to the second reference waveform generator 40 at a carrier frequency fc
It is a carrier pattern generator that sends out information.

Next, the operation of the present invention will be explained.

First, FIG. 2 will be explained. First, if the characteristics of the driven rock 20 are known and the V/f pattern (output pressure/output frequency ratio) to be driven is determined, then at each output frequency fo, the output current Io level can be adjusted. The load power factor can be predicted in advance.

Therefore, by storing the load power factor data corresponding to the output current ■0 for each output frequency fo in advance, the output current level can be detected without comparing the output current waveform and the output voltage waveform (or reference voltage waveform). The load power factor angle φ can be estimated simply by FIG. 2 shows an example in which current levels are detected from two-phase output currents of a three-phase power supply and the power factor angle φ is estimated from a power factor data table.

Further, FIG. 3 shows an example in which the power factor angle is detected by comparing the output current for one phase with the reference waveform of the corresponding phase.

FIG. 4 is a diagram showing how the short-circuit prevention period Td affects one phase (for example, U phase) when the power factor angle is φ at a certain output frequency io, and how to correct it. That is, FIG. 4(a) shows the relationship between the output voltage reference (first reference waveform generator 30) Vo and the output current at the power factor angle φ, and FIG. (c) shows the resulting output voltage waveform. Further, (d) shows the output waveform of the second reference waveform generator 40 generated to eliminate this waveform distortion, and (e) shows the output of the first reference waveform generator 30 and the output waveform of the second reference waveform generator 40. This shows an h1 clay shape in which the outputs of are combined with a phase difference of φ.

The peak value of the rectangular wave voltage component in (b) is as described above (b
) with the same peak value and reversed polarity.

Both voltages are ′ with respect to the virtual neutral point of the inverter input section.
Shown as position.

Next, the operation shown in FIG. 1 will be explained. It is now assumed that the inverter device is operated at an output frequency fo, an output voltage vO, a carrier frequency fc, and an output current of 0.

Therefore, the power factor detector 50 detects the υ load power factor angle φ by detecting the output current 0. First reference wave generator 30
In response to the fo command and the Vo command, the second reference waveform generator 40 generates a first reference waveform in the form of a sine wave, and the second reference waveform generator 40 generates a rectangular waveform having a wave height proportional to the fo command and the gear rear pattern generator 90. A second reference waveform is generated.

The synthesizer 60 receives the power factor angle φ+'A information from the power factor detector 50 and synthesizes the outputs of the first and second reference waveform generators 30 and 40 as shown in FIG. 4(e). , outputs reference waveforms for three phases to the PWM signal generator 70. PwM signal generator 7
0, by comparing the output of the composite ¥560 and the carrier of the carrier pattern generator 90, the switching pattern of each controllable element is determined and output to the drive circuit 80 as shown in the conventional example. The operation of the drive circuit 80 is similar to the conventional example.

Further, the same operation is performed when the load of the inverter changes or when the inverter output fo changes.

Therefore, in any situation, the influence of the short-circuit prevention period Td can be corrected, so there is no output waveform distortion, and there is no output voltage drop due to load increase, resulting in smooth output.
Moreover, an inverter device that can stably ensure output torque characteristics can be obtained.

In addition, in the above embodiment, the case where the inverter input DC α pressure is fixed (Vdc) is shown, but even in an example where Vdc changes, the pressure waveform can be obtained using the Vdc information in the second reference waveform generator. Therefore, the same concept produces the same effect.

In addition, in IPIJ, which detects the output current level (output current) and determines the load power factor, it is also possible to detect the output current level by using the inverter input paper current in place of the output current.

As shown in Figures 2 and 3, power factor detection has been shown as an example in which the inverter load power factor is detected and the reference voltage waveform correction for three phases is performed based on that data. The load power factor corresponding to each phase is calculated separately and based on the power factor information of each phase, the base 4rμ
Voltage waveform correction may also be performed.

〔Effect of the invention〕

As described above, according to the present invention, the output of the first reference voltage generator whose inverter output voltage waveform is raised is corrected according to the inverter load power factor so as to eliminate the influence of the short-circuit prevention period Td. Since the PWM signal is generated, the simple device 1 has the advantage of being able to operate smoothly and stably without compromising the torque and productivity of the motor.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a pulse width modulation type inverter device according to an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing a specific example of power factor detection, and FIG. 4 is a reference waveform of the present invention. An explanatory diagram of the correction method, Fig. 5 is a block diagram showing a conventional pulse width modulation type inverter device, Fig. 6 is a waveform diagram of a general PWM operation, and Fig. 7 is an explanatory diagram showing the influence of the short circuit prevention period Td. It is. In the figure, 20 is an electric motor, 30 is a first reference waveform generator, 40 is a second reference waveform generator, 50 is a power factor detector,
60 is a synthesizer, 70 is a PWM signal generator, 80 is a drive circuit, and 90 is a carrier pattern generator.

Claims (3)

[Claims] (1) In a pulse width modulation type inverter device that outputs alternating current of variable frequency and variable voltage based on an output frequency command and an output voltage command, a main reference voltage waveform is output based on the output frequency command and output voltage command. A first reference waveform generator, a second reference waveform generator that outputs a secondary reference voltage waveform based on the output frequency command, and a power factor detector that detects the load power factor of the inverter device are provided. , the outputs of the first reference waveform generator and the second reference waveform generator are combined by a combiner based on the output of the power factor detector, and the output signal of the combiner is combined with the output signal of the carrier pattern generator. 1. A pulse width modulation type inverter device, characterized in that an on/off pattern of an inverter controllable element is determined by comparing a carrier signal with a PWM signal generator. (2) The power factor detector consists of a current level detector that detects an output current level from an output current detection signal, and a power factor storage circuit that receives the output of the current level detector and outputs power factor information. A pulse width modulation type inverter device according to claim 1. (3) The power factor detector detects the power factor by comparing an output current signal of at least one phase with a reference signal of a corresponding phase. Pulse width modulation type inverter device.