JPH0442911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling an inverter using a pulse width modulation (PWM) wave that reduces harmonic components.

In a PWM type inverter, when the output voltage is adjusted by adjusting the DC power supply voltage of the inverter, it becomes possible to operate the inverter with a single basic PWM wave. However, when adjusting the output voltage of the inverter by changing the pulse width of the PWM wave, it is necessary to generate a PWM wave corresponding to the desired output voltage. Therefore, the applicant has developed an inverter device as shown in FIG. This device consists of transistors 1,
In order to drive a three-phase induction motor 8 with a three-phase bridge type inverter consisting of transistors 2, 3, 4, 5, and 6 and a power supply 7, a PWM wave is supplied to the base of each transistor 1 to 6. There is. 9 is an oscillator, 10 is a variable frequency divider that divides the output frequency of the oscillator 9, 11 is an address counter that specifies a read address based on the output of the frequency divider 10, and 12
read-only memories 12 and 13 read out PWM wave data based on the address designation of the address counter 11; read-only memories 12 and 13 are three-phase distribution circuits that form three-phase PWM waves having a constant phase difference based on the data read out from the memory 12; 14, 15, and 16 are inverters for forming inverted signals of three-phase PWM waves; 17 is a control circuit that forms a control signal based on output voltage detection or designation; 18 is a control circuit 17
This is an output circuit for sending out the output of.

The memory 12 stores various PWM wave data in advance, and output voltage detection signals or command circuit 1
Based on the setting signal sent from 9, PWM wave data corresponding to this is output. That is, the control circuit 17 determines the output voltage and output frequency of the inverter based on external information detected or set, and transmits control data for obtaining the output voltage and output frequency to the output circuit. 18 to memory 12 and frequency divider 10. Now, when control data for changing the output frequency is generated from the line 20, the frequency division ratio of the variable frequency divider 10 changes, and a divided output (clock signal) that can obtain a predetermined frequency is sent out. Ru. On the other hand, control data for obtaining the output voltage V is sent to the memory 12 via the line 21, and the control data for obtaining the output voltage V is sent to the memory 12 via the line 21,
Specify data that matches the output voltage V from the wave data. The read counter 11 operates with a clock corresponding to the desired output frequency, and
Read PWM wave data. PWM read out
The wave data is divided into three phases by the three-phase distribution circuit 13.
It is considered to be a PWM wave, for example as shown in Figure 2.
PWM waves have a certain phase difference and line 22, 2
3, 24, and transistors 1, 3, 5
It becomes the base signal of Also, the inverter 14,1
The PWM waves inverted at 5 and 16 become base signals for transistors 2, 4 and 6.

By the way, if various PWM wave data are written in the memory 12 in advance, the requested PWM wave can be generated immediately as needed. It has the disadvantage that a large amount of memory is required.

Therefore, an object of the present invention is to provide a method for PWM controlling an inverter using a small amount of memory.

To achieve the above object, the present invention includes forming first waveform data for obtaining a pulse width modulated wave for setting the output voltage of an inverter to a predetermined value, and writing the first waveform data in a plurality of ways. writing to a first memory selected from readable memories; reading the first waveform data from the first memory; and switching an inverter based on a pulse width modulated wave corresponding to the first waveform data. controlling the switching element, and during the period in which the switching element is being controlled by the first waveform data read from the first memory, controlling the switching element to obtain a pulse width modulated wave to be output next; writing the second waveform data into a second memory of the plurality of memories during a period in which the switching element is controlled by the first waveform data; reading the second waveform data from the memory of No. 2 and controlling the switching element based on a pulse width modulated wave corresponding to the second waveform data;
forming third waveform data for obtaining a pulse width modulated wave to be output next during a period in which the switching element is controlled by the second waveform data; writing the third waveform data into the first memory or another memory other than the second memory among the plurality of memories during a period when the switching element is being controlled; The present invention relates to an inverter control method that includes reading the third waveform data from the other memory and controlling the switching element based on a pulse width modulated wave corresponding to the third waveform data. .

The present invention has the following effects.

(b) All of the PWM wave data necessary for control
Rather than writing it to ROM, the necessary
Since this method uses PWM wave data formed by calculation or the like, it is possible to significantly reduce memory capacity and downsize the device.

(b) Since PWM wave data is written alternately to multiple memories, it is possible to read PWM wave data from another memory while writing PWM wave data to one memory. Therefore,
Processing (calculation) to form PWM wave data
High speed is no longer required, and costs can be reduced.

Next, a motor drive inverter device according to an embodiment of the present invention will be described with reference to FIGS. 3 to 6. However, in FIG. 3, parts that are substantially the same as those in FIG.

In this embodiment, first and second memories 25 and 26 each consisting of a readable and writable random access memory (RAM) are provided, and an electronic switch circuit 27 is provided for selectively connecting the output to the distribution circuit 13. It is being In addition, a switch circuit 28, in order to alternately put the first and second memories 25, 26 into a writing state and a reading state.
29, and a switch circuit 30 for selectively supplying PWM wave data to the memories 25 and 26. Further, a data forming circuit 3 forms data for obtaining a predetermined output voltage and frequency based on a detected value of the output voltage of the inverter or a command signal given from the output voltage command circuit 19.
1. A write control circuit 32 for generating a write address signal and a switching control circuit 33 for a switch are provided.

FIG. 4 schematically shows the data forming circuit 31. As shown in FIG. The data forming circuit 31 is composed of a microprocessor similar to the control circuit 17 shown in FIG. 1, and forms PWM data through digital processing.
The figure is illustratively shown using an analog analogy. When controlling the inverter output voltage to be kept constant, the inverter output voltage is controlled by the rectifier circuit 34.
The reference voltage circuit 3 is rectified by the error amplification circuit 35.
6 and sends an output voltage corresponding to the difference between the two to the sine wave forming circuit 37. The sine wave forming circuit 37 forms a sine wave having an amplitude corresponding to the error output as shown by voltages V ₁ , V ₂ , and V ₃ in FIG. 5, and sends this in digital form to the comparison circuit 38 .
Since the triangular wave voltage V _R shown in FIG. 5 is supplied in digital form to the comparison circuit 38 from the triangular wave generating circuit 39, a digital comparison output P between the two is generated as shown in FIG. Then, data in which the high level of this output P corresponds to a logic "1" and the low level corresponds to a logic "0" is written into the buffer memory 43, and the read control circuit 40
The data is read out under the control of and sent to the first or second memory 25, 26 in FIG. Reference numeral 41 denotes a frequency determining circuit, which outputs data corresponding to the frequency commanded by the command circuit 19 in FIG. 3, and the data for obtaining the frequency determined here is sent to the output circuit 18 in FIG. The signal is sent to the variable frequency divider 10 via the frequency divider 10, and is used to change the frequency division ratio of the frequency divider 10 so that the frequency of the inverter output becomes a predetermined value. The output data of the frequency determining circuit 41 is also sent to the reference voltage circuit 36, and the reference voltage is controlled so as to obtain the frequency-voltage relationship shown in FIG. If V and V have the relationship shown in FIG. 6, the motor 8 can be driven with a constant torque. Since the command circuit 19 in FIG. 3 is also connected to the error amplification circuit 35 through the contact (b) of the switch 42, the control voltage determined by external information is inputted and PWM according
It is also possible to form wave data.

When controlling the inverter output voltage to be kept constant using a device configured as shown in Figs. 3 and 4, since the inverter output voltage is initially zero, there is no error that increases the output voltage. An output is obtained from the error amplification circuit 35, a corresponding sine wave is formed in the sine wave forming circuit, this is compared with a triangular wave, and a large pulse width is output from the comparison circuit 38.
PWM wave data is obtained and this is switch circuit 3
0 contact (b) to the first memory 25. When writing of data to the first PWM wave data memory 25 is completed, the switching control circuit 3
3 responds to this, switch circuits 27, 28, 2
Contacts (b) at 9 and 30 are turned off and contact (a) is turned on instead, as shown in FIG. As a result, the first PWM wave data written in the first memory 25 is read out under the control of the read counter 11 and sent to the distribution circuit. As a result, the bridge type inverter made up of transistors 1 to 6 is driven by the first PWM wave data. In this embodiment, one cycle of PWM wave data is written in the first and second memories 25 and 26, and the data can be read out repeatedly. contact
While (a) is on, the PWM control state is maintained based on the first PWM wave data. This first
While being controlled by PWM wave data, the inverter output voltage is detected, and the second
PWM wave data is formed and written to the second memory 26 under the control of the write control circuit 32. Then, when writing of the second PWM wave data to the second memory 26 is completed,
The switch circuits 27 and 2 are controlled by the switching control circuit 33.
Contacts (b) of 8, 29, and 30 are turned on, and the second
The second PWM wave data from the memory 26 is read out, and transistors 1 to 6 are controlled based on this. Of course, the first PWM wave data and the second
The PWM wave data may be the same, and in this case, the same PWM wave will continue to be obtained.

While the second PWM wave data is being read from the second memory 26, third PWM wave data is formed based on the detection of the output voltage and is written into the first memory 25. When this writing is completed, the switch circuits 27 and 2
Contacts (a) of 8, 29, and 30 are turned on, and the third
PWM wave data is read. In such control, the sine wave data input to the comparator circuit 38 changes according to changes in the output voltage, and when the output voltage is higher than the reference voltage, the voltage V is lower than the reference sine wave voltage _V1 . ₃ is generated, and conversely, when the output voltage is low, a high voltage V ₃ is generated, and the width of the PWM wave pulse changes based on the comparison with the triangular wave voltage _VR .

Exactly the same operation occurs when the contents of the memories 25 and 26 are changed by a command signal. That is, if a voltage is set in the command circuit 19 or a voltage corresponding to this is supplied as a command signal based on the detection of various external information, PWM wave data corresponding to this is formed, and, for example, the first memory 25 will be written to. Then, while data is being read from the first memory 25, data based on the next command is written to the second memory 26.

As is clear from the above, according to this example,
By only providing two memories 25 and 26, various
It becomes possible to output PWM wave data and simplify the configuration.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto and can be further modified. For example, the waveform data written in the memories 25 and 26 may be for half a cycle, and the remaining half cycle may be formed based on this. Furthermore, data for one cycle or more may be written. Further, data may be written to the second memory 26 only when data different from the data in the first memory 25 is formed. Also, the memory 25,
A memory similar to 26 may be further added. Of course, it is also applicable to a single-phase circuit. Alternatively, a configuration may be adopted in which a detection signal or a command signal is directly input to the comparison circuit 38 shown in FIG. Further, in the embodiment, a sine wave is generated using digital values, and a triangular wave is generated using digital values, but an analog processing method may also be used.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional inverter device, Figure 2 is a waveform diagram showing an example of a PWM wave, and Figure 3 is a waveform diagram showing an example of a PWM wave.
The figure is a block diagram showing a PWM inverter device according to an embodiment of the present invention, FIG. 4 is a block diagram explanatory of the data formation circuit of FIG. 3, and FIG. 5 is a waveform diagram for explaining data formation. , FIG. 6 is a characteristic diagram showing the relationship between voltage and frequency. In addition, in the symbols used in the drawings, 1,
2, 3, 4, 5, 6 are transistors, 19 is a command circuit, 25 is a first memory, 26 is a second memory, 27, 28, 29, 30 are switch circuits, 3
1 is a data forming circuit.

Claims (1)

[Claims] 1. Forming first waveform data for obtaining a pulse width modulated wave for setting the output voltage of the inverter to a predetermined value, and a plurality of memories capable of writing and reading the first waveform data. reading the first waveform data from the first memory and controlling a switching element of an inverter based on a pulse width modulated wave corresponding to the first waveform data; and, during a period in which the switching element is controlled by the first waveform data read from the first memory, second waveform data for obtaining a pulse width modulated wave to be outputted next. writing the second waveform data to a second memory of the plurality of memories during a period in which the switching element is controlled by the first waveform data; and writing the second waveform data to a second memory of the plurality of memories; reading the second waveform data and controlling the switching element based on a pulse width modulated wave corresponding to the second waveform data; , forming third waveform data for obtaining a pulse width modulated wave to be output next; and generating the third waveform data during a period in which the switching element is controlled by the second waveform data. the first memory or the second memory of the plurality of memories;
reading the third waveform data from the first memory or the other memory, and performing the switching based on the pulse width modulated wave corresponding to the third waveform data. An inverter control method comprising: controlling an element;