JPH0824426B2 - Pulse width modulation type inverter device - Google Patents

Description

The present invention relates to a pulse width modulation type inverter device for converting direct current or direct current obtained by converting direct current or alternating current by a forward converter into alternating current of variable frequency and variable voltage. is there.

[Conventional technology]

Figures 5 to 6 show, for example, the conventional pulse width modulation type inverter device shown in 157, Tokai Branch Joint Conference of the Institute of Electrical Engineers of Japan, 151, "Influence of the upper and lower arm short circuit prevention period of the PWM inverter on the waveform". In the diagram, Vd
c is a DC power supply obtained by converting AC into a forward converter, or DC power supply such as battery, 10 is a main circuit unit (inverter converter unit) of an inverter device for converting the DC power supply Vdc into variable frequency and variable voltage AC , 20 is a motor such as an induction motor driven by the main circuit unit 10, 30 is a reference voltage for each phase of the inverter, which receives an output frequency command (hereinafter referred to as fo command) and an output voltage command (hereinafter referred to as Vo command) A first reference waveform generator 70 for outputting a waveform signal is a pulse width modulation (hereinafter referred to as PWM) which determines a switching pattern of a controllable element by comparing the first reference waveform generator 30 with a carrier signal. Signal generator, 80 is a PWM signal generator 70
Is a drive circuit for driving the controllable element upon receipt of the signal.
90 is a carrier pattern generator that outputs a carrier waveform of a carrier frequency corresponding to the fo command. Reference numeral 100 is a V / f pattern generator that receives a fo command and outputs a Vo command.

Next, the operation will be described. First, FIG. 6 shows the PWM operation of one phase (U phase) out of three AC phases. When the first reference waveform generator 30 receives the fo command and the Vo command, it outputs the reference voltage waveform Vo as shown in FIG. 6 (a). PWM
The signal generator 70 is a carrier signal as shown in FIG. 6 (a).
The switching pattern is determined by comparing Vc with the reference waveform Vo. FIG. 6 (b) shows the upper and lower controllable elements (eg, transistors) T _UP and T _UN of the U phase (the main circuit section 1 in FIG. 5).
0) switching pattern, U _PO , U _NO . Reference voltage
ON when Vo is larger than carrier Vc, OFF when Vo is smaller
U _PO is determined as, and its reverse signal is U _NO . Other V
For the W and W phases, the same carrier and the reference voltage waveform with a phase difference of 120 ° or 240 ° are compared to obtain the same.

Although off pattern is determined as described above, on-off signals U _P which is output to the drive circuit 80, U _N (FIG. 6 (c)
Indicates a short circuit prevention period Td in order to prevent short circuit of the U-phase upper and lower elements due to the switching delay of the controllable element.
A so-called short-circuit prevention process is performed in which a period for turning off both lower elements is provided. Td is usually set to a sufficiently large value in consideration of the delay of the drive circuit and controllable elements. The same applies to V-phase and W-phase signals. Drive circuit 80 drives the controllable element receiving off signal from the PWM signal generator 70 (U _P, U _N, etc.). As a result, the inverter is in the operating state with the frequency fo and the voltage Vo.

To simplify the explanation, ignoring the delay of the drive circuit 80 and the controllable element main circuit section 10, during the short circuit prevention period Td,
Since it is a non-control period in which both the upper and lower controllable elements are turned off, the potential of the output terminal is determined by the function of the freewheeling diode depending on the polarity of the output current. That is, a positive output current has a negative potential, and a negative output current has a positive potential. This state is shown in FIGS. 7 (a) and 7 (b). The figure shows U
It is expressed as the potential with respect to the phase with respect to the virtual neutral point of the inverse converter input.

Therefore, for example, the output voltage waveform of the U phase does not become an ideal sine wave according to the on / off patterns U _PO and U _NO , but has distortion. This is shown in FIGS. 6 (d) and 6 (e). (E) shows that the influence of the above-mentioned short circuit prevention period Td appears according to the output current polarity. If taken as an average, it can be captured as a rectangular waveform voltage waveform of the same fo. The output voltage shown in (d) is finally a combination of the ideal sine wave determined from the PWM signals U _PO and U _NO and the influence voltage of Td shown in (e). If this situation is grasped by the voltage between the output lines, it can be expressed by equation (1).

Here, T _UV ; U-V line voltage, Vdc; Inverter DC part voltage, A, B; Voltage output coefficient, φ; Power factor angle, Td; Short circuit prevention period,
Tc; PWM carrier period. In the formula (1), the first
The term represents the voltage component 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 1 / Tc.

Then, the effects of the short circuit prevention period Td are summarized as follows.

(1) Since the inverter output voltage does not have an ideal sine wave, the torque ripple and rotation ripple of the motor increase, and the vibration increases.

(2) As the load increases, the power factor improves (φ → small)
Since the phases of the first term and the second term of the equation (1) approach each other, the output voltage decreases. As a result, the output torque characteristic deteriorates.

(3) The electric motor cannot be driven stably.

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

[Problems to be solved by the invention]

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, and the distortion waveform Becomes As a result, there are problems that the torque ripple and the rotation ripple of the electric motor are increased, the output torque is decreased, and the electric motor cannot be driven stably in a low frequency region where the output voltage is low.

The present invention has been made to solve the above problems, and a pulse width modulation type inverter device capable of smoothly and stably driving an electric motor without impairing output torque characteristics even in a low frequency region where the output voltage is low. Aim to get.

[Means for solving problems]

The pulse width modulation type inverter device according to the present invention includes, in addition to the first reference waveform generator for controlling the output voltage waveform, the second reference waveform generator for correcting the output voltage waveform, and the power factor detection of the inverter load. And a container.

[Work]

In the PWM circuit according to the present invention, the power factor angle is detected by the power factor detector of the inverter load, and when the power factor is detected, the first reference waveform generator and the first reference waveform generator are provided so as to cancel the influence of the expected short circuit prevention period Td. Create a PWM signal by synthesizing the output waveforms with the reference waveform generator of 2.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, parts that are the same as those in FIG. 5 are shown with the same reference numerals, and in FIG. 1, 40 receives the fo command and the output of the carrier pattern generator 90 to generate a reference waveform for output waveform correction. A second reference waveform generator, 50 detects an inverter output current, stores the power factor information in a power factor memory circuit, and based on the information, detects a load power factor, 60 is a power factor detector. The first reference waveform generator 30 receives the power factor information from the factor detector 50.
Is combined with the output of the second reference waveform generator 40 by shifting by the power factor angle. 90 receives fo command fo
PWM the carrier pattern at the carrier frequency fc corresponding to
Second reference waveform generator while sending to the signal generator 70
A carrier pattern generator that sends carrier frequency fc information to 40.

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

First, FIG. 2 will be described. First, if the characteristics of the driven motor 20 are known and the V / f pattern (output voltage / output frequency ratio) to be driven is determined, the load current corresponding to the output current Io level is preset at each output frequency fo. Power factor can be predicted. In addition, the load power factor can be estimated by the load current flowing through the motor if the motor (rated), the voltage applied to the motor, and the frequency are known. This is because the load power factor is determined by the motor (rating), the voltage applied to the motor, the frequency, and the load current. Therefore, it is possible to predict the load power factor from the load current by selecting the drive motor in advance, determining the driving voltage and frequency, and measuring the relationship between the load current and the load power factor. Therefore, the output current Io is preset for each output frequency fo.
If the corresponding load power factor data is stored, the load power factor angle φ can be estimated only by detecting the output current level without comparing the output current waveform and the output voltage waveform (or the reference voltage waveform). FIG. 2 shows an example in which the current level is detected from the output currents of the two phases of the three-phase power supply and the power factor angle φ is estimated from the power factor data table.

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

FIG. 4 is a diagram showing a state of the influence of the short-circuit prevention period Td for one phase (for example, U phase) when the power factor angle at a certain output frequency fo is φ, and a method of correcting it. That is, FIG. 4 (a) shows a relationship diagram in which the output voltage reference (first reference waveform generator 30) Vo and the output current are the power factor angle φ, and FIG. 4 (b) shows the influence voltage of Td. , (C) show the resulting output voltage waveforms. Further, (d) is an output waveform of the second reference waveform generator 40 generated to eliminate this waveform distortion, and (e) is an output waveform of the first reference waveform generator 30 and the second reference waveform generator 40. 3 shows a reference waveform in which the output of 1 is combined with the phase difference of φ.

The rectangular wave voltage component crest value in (b) is proportional to Vdc · Td / Tc as described above. Therefore, (d) has the same crest value as (b) but the polarity is inverted. All voltages are given as potentials relative to the virtual neutral point of the inverse transformer input.

Next, the operation of FIG. 1 will be described. Now, the inverter device has output frequency fo, output voltage Vo, carrier frequency fc,
It is assumed that the operation is performed with the output current Io. So power factor detector
50 detects the load power factor angle φ by detecting the output current Io. The first reference wave generator 30 receives the fo command and Vo command to generate a sinusoidal first reference waveform, and the second reference waveform generator 40 outputs the fo command and the carrier pattern generator 90. Receiving the fc information (Tc = 1 / fc), it generates a rectangular wave-shaped second reference waveform having a peak value proportional to Vdc · Td / Tc.

The combiner 60 receives the power factor angle φ information of the power factor detector 50,
The outputs of the first and second reference waveform generators 30 and 40 are combined as shown in FIG. 4 (e), and the reference waveforms for three phases are output to the PWM signal generator 70. In the PWM signal generator 70, by comparing the output of the synthesizer 60 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 that of the conventional example.

The same operation is performed when the load of the inverter changes and when the output fo of the inverter changes. Therefore, in any state, since the influence of the short circuit prevention period Td can be corrected, there is no output waveform distortion, and there is no output voltage drop due to load increase.
An inverter device capable of ensuring output torque characteristics can be obtained.

Further, in the above embodiment, the case where the inverse converter input DC voltage is fixed (Vdc) is shown, but even in the example in which Vdc changes, Vdc information can also be input to the second reference waveform generator to obtain Vdc information.
Since the correction waveform of the peak value proportional to dc · Td / Tc is obtained, the same effect can be obtained with the completely same idea.

Further, in the example in which the output current level is detected from the output current and the load power factor is obtained, the output current level can be detected by using the inverse converter input current instead of the output current.

The power factor detection is shown as an example in which the inverter load power factor is detected as shown in FIGS. 2 and 3 and the reference voltage waveforms for three phases are corrected based on the data. The load power factor corresponding to each phase may be separately obtained and the reference voltage waveform correction may be performed based on each power factor information.

〔The invention's effect〕

As described above, according to the present invention, the output of the first reference voltage generator for controlling the inverter output voltage waveform and the output of the second reference waveform generator are used as power factor information from the power factor detector. Based on this, the power factor angle is shifted and combined by the combiner, and the reference signals for three phases and the carrier signal of the carrier pattern generator are input from this combiner to the PWM signal generator, and the on / off pattern of the inverter controllable element is set. Since it is configured to determine, the signal processing circuit on the input side of the PWM signal generator is composed of one first and second reference waveform generator, a power factor detector, a combiner, and a carrier pattern generator, respectively. Therefore, an imbalance of three phases due to variations in circuit components does not occur, and the torque characteristic of the electric motor, which is a load, is not impaired by a simple device. Further, there is an effect that the operation can be performed smoothly and stably.

Further, the power factor detector is a current level detector that detects a current level from the output currents of the two phases of the three-phase power source, and a power factor data table that receives the output of the current level detector and outputs the power factor information. With this configuration, the load power factor angle can be estimated only by detecting the output current level, and the remarkable effect that the configuration for eliminating the influence of the short circuit prevention period can be further simplified is obtained. .

[Brief description 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 concrete example of power factor detection, and FIG. 4 is a reference waveform of the present invention. FIG. 5 is a block diagram showing a conventional pulse width modulation type inverter device, FIG. 6 is a waveform diagram of general PWM operation, and FIG. 7 is an explanatory diagram showing the influence of the short circuit prevention period Td. 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 combiner, 70 is a PWM signal generator, 80 is a drive circuit, and 90 is a carrier pattern generator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigezo Kuriyama 5-1-14 Yataminami, Higashi-ku, Nagoya-shi, Aichi Mitsubishi Electric Corporation Nagoya Works (56) Reference JP-A-59-123478 (JP, A) ) JP-A-57-206281 (JP, A) JP-A-60-118083 (JP, A)

Claims (1)

[Claims] 1. In a pulse width modulation type inverter device for converting direct current into alternating current of variable frequency and variable voltage, a first reference for outputting a main reference voltage waveform based on an output frequency command and an output voltage command given from the outside. A waveform generator,
A second reference waveform generator that outputs a subordinate reference voltage waveform based on the output frequency command and a carrier signal of the carrier pattern generator; a power factor detector that detects a load power factor of the inverter device; A synthesizer for synthesizing the output of the first reference waveform generator and the output of the second reference waveform generator by shifting the power factor angle based on the power factor information from the power factor detector; The reference signals for the three phases and the carrier signal from the carrier pattern generator are input to determine the on / off pattern of the inverter controllable element.
The power factor detector is provided with a PWM signal generator, and the power factor detector outputs the current factor detector for detecting the current level from the output currents of the two phases of the three-phase power source and the output of the current level detector. A pulse width modulation type inverter device comprising a power factor data table.