JPS6338951B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter control method, and more particularly to a pulse width modulation (PWM) method for multiplexed inverters.

FIG. 1 shows an example of a unit inverter that is a component of a multiplexed inverter to which the present invention is applied. In Fig. 1, 1 is an AC power supply, 2 is a rectifier whose phase can be controlled, 3 is a smoothing capacitor for smoothing the voltage,
4 is a switching element Su, Sv, Sw, Sx, Sy,
5 is a load, which is an inverse converter constituted by Sz and converts direct current into alternating current with a variable frequency.

FIG. 2 shows operating waveforms of the unit inverter shown in FIG. 1. FIG. 2a shows switching elements Su, Sv, Sw, Sx, Sy, Sz that constitute the inverse converter 4.
The on-period is shown, and the case of 120° energization is taken as an example.
FIG. 2b shows each phase output voltage waveform eu _-0 , ev _-0 , ew _-0 of the unit inverter.

FIG. 3 shows another example of a unit inverter which is a component of a multiplexed inverter to which the present invention is applied. In Fig. 3, 1 is an AC power supply, 2 is a rectifier whose phase can be controlled, 6 is a DC reactor that smoothes the current, and 4 is a switching element Su, Sv, Sw, Sx,
An inverter 5 is a load, which is composed of Sy and Sz and converts direct current into alternating current with variable frequency.

FIG. 4 shows operating waveforms of the unit inverter shown in FIG. 3. FIG. 4c shows switching elements Su, Sv, Sw, Sx, Sy, and Sz constituting the inverse converter 4.
FIG. 4b shows the output current waveforms iu, iv, iw of each phase of the unit inverter. The current waveforms iu, iv, iw shown in Fig. 4b are the same as the voltage waveforms eu _-0 , ev _-0 , ew _-0 shown in Fig. 2b, and the relationship between voltage and current is reversed. It is something that Therefore, the following explanation will be given using the voltage waveform shown in FIG. 2 as an example, but a unit inverter having the configuration shown in FIG. 3 can also be used by simply replacing the voltage waveform with a current waveform.

FIG. 5 shows switching elements Su, which constitute the inverter 4, using the unit inverter shown in FIG.
FIG. 3 is a diagram for explaining a method of pulse width modulating (PWM) the output voltage by controlling the on-periods of Sv, Sw, Sx, Sy, and Sz. FIG. 5a shows six switching elements Su, which constitute the inverse converter.
A diagram showing the on-periods of Sv, Sw, Sx, Sy, and Sz, and Figure 5b shows the output voltage waveforms eu _-0 , ev _-0 ,
It is a diagram showing ew _-0 , and each corresponds to one cycle period (360°) of the inverter output. An explanation will be given by taking as an example the case of commutation from the switching element Su to Sv in FIG. 5a.

In FIG. 2a, the commutation between Su and Sv is performed only once in the direction from Su to Sv at 120°. On the other hand, in Fig. 5a, the commutation between Su and Sv is always carried out an odd number of times around the point of 120° (Fig. 5a shows the case where 5 rotations are made as an example), and the final automatically transitions to the Sv on period. The period during which this odd number of commutations takes place (PWM
The period) is limited to a period of 60° in total with 30° before and after 120°, and if it becomes wider than that, it overlaps with the ON period of the switching element Sx or Sy, resulting in a DC short circuit. Similarly, commutation between other switching elements is completed after an odd number of commutations, and finally the transition to the next phase is completed. If we focus on one switching element, there is a minimum period of 60 degrees during which it should always remain on, and there are PWM periods of maximum 60 degrees before and after that, for a total of 120 degrees. As an example, if we focus on Su, the period from 30° to 90° is the period in which it must remain on, and during this period, Sy and Sz are
It is in PWM period. And before this period
60° is Sw and PWM period, after this period 60° is
This is the PWM period with Sv. By controlling the switching elements on and off as described above, a pulse width modulated output voltage waveform shown in FIG. 5b is obtained.

Next, FIG. 6 shows an example of a multiplex inverter to which the present invention is applied. A multiplex inverter is one in which two or more unit inverters as shown in FIG. 1 or 3 are connected together to improve the output waveform and expand the inverter capacity. Figure 6 shows an example of a duplex inverter using two unit inverters 10 and 20 shown in Figure 1, with transformers 17 and 27 on the output side.
The voltages are synthesized and supplied to the load 5. This 2
Figure 7 shows the operating waveforms when the multiplexed inverter is operated using the normal 120° energization method.

FIG. 7a shows switching elements Su ₁ , Sv ₁ , Sw ₁ , Sx ₁ , Sr ₁ , which constitute the unit inverter 10.
FIG. 7b shows the on period of Sz ₁ , and FIG. 7b shows the switching elements Su ₂ ,
The on-periods of Sv ₂ , Sw ₂ , Sx ₂ , Sy ₂ , and Sz ₂ are shown.
Both have a phase difference of 30 degrees, so the output waveforms of the two unit inverters have a phase difference of 30 degrees.
The phase difference α between unit inverters can be set arbitrarily, but in the case of a duplex inverter, it is usually set to α = 30°,
In the case of a triplex inverter, α is often set to 20°. FIG. 7c shows the output voltage waveform of the unit inverter 10 whose on-period is controlled as shown in a, and FIG. 7d shows the output voltage waveform of the unit inverter 20 whose on-period is controlled as shown in b. be. Figure 7e
is a waveform obtained by simply synthesizing the above c and d using transformers 17 and 18, and this is supplied to the load 5. When compared with the output voltage waveform of the unit inverter shown in FIG. 2b, FIG. 7e shows that the waveform has a large number of steps in one cycle and is close to a sine wave. If the number of connected unit inverters is increased and multiplexing is performed, the output waveform will become more similar to a sine wave. However, promoting multiplexing in order to improve the output waveform has the problem of increasing the cost and increasing the size of the inverter device, and it is usually used in a duplex or triplex configuration. In this case, when the motor load is driven at a low frequency by an inverter, there are problems such as large torque ripples that occur and prevent smooth rotation, mechanical loads such as vibrations being placed on the load, and a decrease in the amount of generated torque. .

SUMMARY OF THE INVENTION The object of the present invention has been made in view of the above drawbacks, and is a multiplexed inverter control that eliminates the above drawbacks by incorporating the pulse width modulation into the multiplexed inverter and bringing the output waveform closer to a sine wave. The purpose is to provide a method.

Figure 8 shows the duplex inverter shown in Figure 6.
An example of PWM control is shown below. FIG. 8a shows switching elements constituting the unit inverter 10.
FIG. 8b shows the ON period of Su ₁ , Sv ₁ , Sw ₁ , Sx ₁ , Sy ₁ , Sz ₁ , and FIG. 8b shows the switching elements Su ₂ , Sv ₂ , Sw ₂ , Sx ₂ , Sy ₂ ,
Shows the on period of Sz ₂ . As mentioned above, the phase difference α between the unit inverters 10 and 20 can be arbitrarily determined, but in FIG. 8, the explanation will be made assuming that α=30°. Taking the case of commutation from the switching element Su ₁ to Sv ₁ as an example, the commutation between Su ₁ and Sv ₁ in FIG.
Eventually it will move to the on period of Sv ₁ . As mentioned above, the PWM period during which this odd number of commutations is performed can be 30 degrees before and after the 120 degree point, for a total of 60 degrees, but the operation is performed with a phase difference α of 30 degrees. In order to avoid overlapping the PWM periods of the two unit inverters 10 and 20, the PWM periods must be
It is necessary to limit the period to a total of 30° with α/2 = 15° before and after the 120° point. If we focus on a single switching element, there is a minimum period of 90 degrees during which it must remain on at all times, and before and after that, the above-mentioned
Maximum PWM period is 30° (= α), total 60° (=
2α) Exists. As an example, focusing on Su ₁ , the period from 15° to 105° is the period in which it must be kept on, and during this period, the same unit inverter 10
Sy ₁ and Sz ₁ and Sw ₂ of the other unit inverter and
Includes Su ₂ or Sy ₂ and Sz ₂ PWM periods. The 30° (=α) before this period is Sw ₁ and the PWM period, and the after
30° (=α) is the PWM period with Sv ₁ . More than ₁
Although the explanation has focused on the above, the same applies to other switching elements. By on/off control of these switching elements, the pulse width modulated output voltage waveforms shown in FIG. 8c and d are obtained from the unit inverters 10 and 20. FIG. 8e shows a waveform obtained by simply combining the output voltages of c and d using transformers 17 and 27, and this waveform is supplied to the load 5.
In fact, by increasing the PWM frequency, the output waveform is further improved. As an example, FIG. 9 shows the waveform when the PWM frequency is increased. 9th
The figure shows 1/6 (=60°) from one cycle of the inverter output.
This is an enlarged version of Su ₁ of unit inverter 10 and
Sv ₁ and 2 sets of Su ₂ and Sv ₂ of unit inverter 20
Contains PWM period. 9c, d, and e show the output voltage waveform of the unit inverter 10, the output voltage waveform of the unit inverter 20, and the overall output voltage waveform, respectively. The details of the operation are the same as those in FIG. 8, so they will be omitted.

FIGS. 10, 11, and 12 show different examples of multiplex inverters to which the present invention can be applied. 10th
In the figure, 10, 20, and 30 are unit inverters shown in FIG. 1, and 17, 27, and 37 are transformers for synthesizing the inverter output voltages. 40, 50, 60 in Figures 11 and 12
is the unit inverter shown in Fig. 3, and 47,5
7 and 67 are transformers for combining inverter output currents. As mentioned above, Fig. 11 and 1
In the example of FIG. 2, the same explanation holds if the output voltage waveforms in FIGS. 8 and 9 are viewed as output current waveforms.

Note that the multiplex inverter to which the present invention is applied is the sixth one.
The present invention is not limited to those shown in FIGS. 10, 11, and 12. Transformer 1 on the inverter output side
The present invention can be carried out even if the output voltage or current waveform differs depending on the wiring of 7, 27, 37, 47, 57, and 67, and the same applies even when a transformer is not provided on the inverter output side but a transformer is provided on the input side. It is.

As explained above, according to the present invention, pulse width modulation is performed to further improve the output waveform of a multiplex inverter, and even when driving an electric motor at an extremely low frequency, smooth output with less torque ripple can be achieved. rotation can be maintained.

[Brief explanation of the drawing]

Figure 1 shows an example of a unit inverter that is a component of a multiplex inverter, Figure 2 shows its operating waveforms, and Figure 3 shows its operating waveforms.
The figure shows another example of the unit inverter, Figure 4 shows its operating waveform, and Figure 5 shows the unit inverter shown in Figure 1.
PWM operation waveforms, Fig. 6 is an example of a duplex inverter to which the present invention is applied, Fig. 7 is an operation waveform when the duplex inverter of Fig. 6 is operated in the conventional 120° conduction operation, Fig. 8 9 is an enlarged view of FIG. 8, and FIG. 10 to 1 are operating waveforms when the present invention is implemented.
FIG. 2 shows different examples of multiplexed inverters to which the present invention is applied. 1... AC power supply, 2... Phase controllable rectifier, 3... Smoothing capacitor, 4... Inverter, 5
...Load, 6...DC reactor, 10, 20,
30...Unit inverter shown in FIG. 1, 40,
50, 60... Unit inverter shown in Figure 3,
17, 27, 37...Transformer for inverter output voltage synthesis, 47,57,67...Transformer for inverter output current synthesis, Su, Sv, Sw, Sx, Sy,
Sz...Switching element constituting the inverter 4 or on period of the element, Su ₁ , Sv ₁ , Sw ₁ ,
Sx ₁ , Sy ₁ , Sz ₁ ... Switching elements constituting the inverse converter 4 in the unit inverters 10, 40 or on period of the elements, Su ₂ , Sv ₂ , Sw ₂ , Sx ₂ , Sy ₂ ,
Sz ₂ ... Switching element constituting the inverter 4 in the unit inverter 20, 50 or on period of the element, eu _-0 , ev _-0 , ew _-0 ... Inverter output voltage, eu _1- D, ev _1- D, ew _1- D... Output voltage of unit inverter 10, eu _2-0 , ev _2-0 , ew _2-0 ... Output voltage of unit inverter 20, Su ₂ , Sv ₃ , Sw ₃ ,
Sx ₃ , Sy ₃ , Sz ₃ . . . switching elements constituting the inverter 4 in the unit inverters 30, 60, or on-periods of the elements.

Claims (1)

[Claims] 1. In a multiplexed inverter in which two or more n sets of three-phase bridge-connected 120° energizing type inverter circuits are connected in parallel, each inverter circuit is energized and controlled with a predetermined phase difference α°, Between the end of continuous energization of a certain switching element that is continuously energized in the inverter circuit and the start of continuous energization of another switching element that is continuously energized next, 1. A method for controlling a multiplexed inverter, comprising: providing a period in which the switching elements are alternately energized, and controlling the period in which the alternately energizing element is within the predetermined phase difference α°.