JPS58198165A - Detecting method for current of pwm converter - Google Patents

Abstract

PURPOSE:To obtain the detected current value of the fundamental wave component of an output current without influence of pulsating component by detecting the output current of a PWM converter when a carrier signal is in the vicinity of the maximum amplitude. CONSTITUTION:A microcomputer 9 detects the speed and current of an induction motor 6, and executes the speed control process to allow the speed of an induction motor 6 to respond to the speed instruction value. A voltage instruction value to be applied to the motor 6 is outputted by the control process. An instantaneous voltage generator 14 generates an instantaneous voltage signal (modulation signal) of sinusoidal waveform in response to the voltage instruction value. The output signal of a PWM inverter 1 is detected when the carrier signal is in the vicinity of the maximum amplitude by comparing the modulation signal with a triangular waveform carrier signal which is outputted from a carrier signal generator 15.

Description

Detailed Description of the Invention The present invention is a PWM transformer that detects the output wL current of a PWM transformer that switches DC voltage and controls the output voltage to a desired value.
The present invention relates to a method for detecting 11LflL of a converter.

As a power converter that switches the DC voltage and controls the fundamental wave component of the output voltage to a desired value, pulse width modulation (hereinafter referred to as PWM) is used for variable speed driving of induction motors.
There are choppers for driving inverters and DC motors.

Generally, the output current of these power converters has a waveform in which a pulsating component is superimposed on a fundamental wave component due to the switching output voltage. In order to detect such an output current and perform current control, it is desirable to extract only the fundamental wave component as much as possible and take it out as a detected value that is less affected by the pulsating component.

On the other hand, a digital control device using a microprocessor or the like executes current control at predetermined intervals. Detection of the output current of the power converter is also performed at each control cycle. Therefore, the value obtained varies greatly depending on when the pulsating power converter output current is detected. Such a detected value is inappropriate as a detected value for current control.

Conventionally, in order to remove the pulsating component of the '#LfIL detected value, the current detected value of the current detector is smoothed using a low-pass filter. By taking in a smoothed current detection value with less pulsation component every control cycle, it becomes possible to detect the fundamental wave component of the output tm of the power converter.

However, when a low-pass filter is used, if the frequencies of the fundamental wave component and the pulsating component to be removed are close to each other, it becomes difficult for the filter to accurately detect the fundamental wave component and remove the pulsating component. Another problem is that the phase of the detected current value is delayed due to the time delay caused by the filter, making it impossible to detect it as an instantaneous current value.

To solve these problems, and to detect the firing time (ltk) with less influence of pulsation components and no delay in each control cycle, we have developed a method that synchronizes with the switching signal (ignition pulse signal) of the power converter. According to this method, in order to detect the current value at the axis of the current wave shadow that pulsates in response to the ignition pulse signal,
A current value that is not affected by the pulse JIIJ component can be obtained without using a low-pass filter or the like. Furthermore, the obtained current value is not passed through a filter, so there is no phase delay and it is the instantaneous current value at the time of detection.

The method of detecting current in synchronization with the nine firing pulse reconnaissances described above is suitable for current detection in devices where firing pulses are output only once in a predetermined period, such as chopper control devices and thyristor V-honored devices. Since the period is almost constant, 1
There is no problem with the time required for current detection or the time required for control processing. However, in a PWM inverter in which the time interval of a switching signal is modulated, the current detection period varies in accordance with the switching signal. Therefore, when the on-off time interval is modulated and narrowed, the pulse interval may become narrower than the time required for one current detection. Furthermore, when performing control processing in synchronization with a switching signal, there is a problem that the pulse interval is shorter than the time required for one control processing at a point in time when the pulse interval is narrow, resulting in insufficient processing time. .

In addition, the method of detecting the output current of the power converter in synchronization with the ignition pulse can realize current detection with less influence of pulsation components, but the detected value is at the peak of the current pulsation, which corresponds to the time of the ignition pulse. There is also a drawback that an average current detection value representing the fundamental wave component of the output current cannot be obtained.

The present invention has been made in response to the above-mentioned problems, and its purpose is to provide a current detection method for a PWM converter that is less affected by pulsation components and can obtain a detected value of the fundamental wave component of the output current. It's about doing.

The special advantage of the present invention is that the output current of the PWM converter is detected when the carrier wave signal, which is the reference signal used to generate the switching signal 11 of the PWM converter, is near the maximum amplitude value. FIG. 1 shows an embodiment of the present invention.

Figure 1 shows an induction motor using a PWM inverter.
This is an example in which

In Figure 1, the PWM inverter 1 has a 35fi power supply 2.
The AC voltage is converted to DC by a forward converter 3, and the DC voltage smoothed by a capacitor 4 is then manually input to the PWM inverter 1.
The DC input voltage is pulse width modulated and applied to the induction motor 6.A U-tary encoder 7 is directly connected to the induction motor 6, and the output pulses of the rotary encoder 7 are sent to the counter 8.
is incremented by 1. A microcomputer (hereinafter abbreviated as microcomputer) 9 reads the count value of the counter 8 at regular intervals and calculates the speed of the induction motor 6. “Fico/
9 executes speed calculation by time interrupt processing every 10 mS, for example. The current flowing through the induction motor 6 is detected by a current detector 10 and inputted to an A/D converter 12 via a multiplexer 11 .

The microcomputer 9 manually inputs the current detection timing signal given as described later and specifies the phase address of the multiplexer. The multiplexer 11 applies the current detection value of the specified phase to the A/D converter 12. When the A/D converter 12 receives an A/D conversion start signal from the microcomputer 9, it converts the detected current value into a digital quantity. When the A/D conversion is completed, the microcomputer 9 takes in and inputs the value as a current detection value. When the current acquisition for one phase is completed, similar processing is performed to acquire current detection values for the other two phases.

These current detection values are taken in between 0.5 and 1 mS. On the other hand, the microcomputer 9 receives and inputs a speed command value from the speed command circuit 13. The speed command values are taken in, for example, at intervals of 10 m8.

The microcomputer 9 detects the speed and current of the induction motor 6 as described above, and executes speed control processing so that the speed of the induction motor 6 responds to the speed command value. Through this control process, a voltage command value to be applied to the induction motor 6 is output. The instantaneous voltage waveform generating circuit 14 generates instantaneous voltage signals (modulated wave signals) of three phases of a sine waveform in accordance with the voltage command value. A comparator 16 compares this modulated wave signal with a triangular waveform carrier signal outputted from a carrier wave signal generation circuit 15, thereby generating a PWM signal for controlling the PWM inverter 1.
I get a signal. By adding this PWM No. 46 to the PWM converter 1, the induction motor 6 can be controlled to the speed command value given from the speed command circuit 13.

FIG. 2 shows the current detection timing signal and P W M 11
A detailed diagram of the circuits 14, 15, and 16 that generate the signals is shown.

The instantaneous voltage waveform generation circuit 14 includes D/A converters 17 and 19.
, 20.90' phase difference, and analog multipliers 21 and 22. Note that FIG. 2 shows only the instantaneous voltage waveform generation circuit for one phase. The instantaneous voltage waveform generation circuit 14 includes a microcomputer 9.
Therefore, in this legend, as a command to generate an instantaneous voltage waveform, the frequency command value fl* of the instantaneous voltage and the instantaneous voltage are set to 2.
Command values Vwrj and Vt* of the magnitude of two components when expressed by two orthogonal coordinate axis components are given. The frequency command value f 1 * is converted into an analog quantity by the D/A converter 17 and applied to the two-phase oscillator 18 .

The two-phase oscillator 18 has a frequency of fl'' and a phase difference of 90'.
Phase sine wave signal sia 2πf l” +ωS2πf t
*Output t. On the other hand, the biaxial acid content of the instantaneous voltage V m
" g V W are each converted into an analog quantity by the D/A converter 19.20. The excitation component command value V of the analog quantity
: is the output signal sin 2 of the two-phase oscillator 18 at the multiplier 21
π7t"t and the multiplication are combined, and the torque component command value ■
- is multiplied by CO32πf 1*t . By adding the outputs of both multipliers 21 and 22, an instantaneous voltage command value v1* for one phase is obtained. The instantaneous voltage command value v1'' is expressed by the following equation.

vl” ” V m”sll 2 πft*l +V
t”(J)82 K f 1*t=V1”5in(2π
ft*t +θv") = (1n) Here, this instantaneous voltage command value v1* is a sinusoidal modulated wave 1g M
becomes.

The carrier wave signal generation circuit 15 includes a clock pulse generator 24,
Up/down counter 25, D/A converter 26, maximum 1
[Comprised of a discrimination circuit 27, a minimum value discrimination circuit 28, an OR circuit 29, and a flip-flop 30.

The operation of the carrier wave signal generation circuit 15 will be explained using FIG. 3. Clock pulses (a) outputted from the clock pulse generator 24 are counted by an f-down counter 25. The count value of the counter 25 changes as shown in FIG. 3(C). The count value of the counter 25 is determined by the maximum value determination circuit 2.
7 is the maximum value set (corresponds to the maximum positive amplitude value of the carrier wave)
When the count value becomes equal to the set maximum value of 11iL, an overflow pulse (b) is output. Pulse (b
) is applied to the flip-flop 30 through the OR circuit 29. Flip-frog 30 changes its output from the "1" level to the "O" level. The counter 25 switches between up-counting and down-counting depending on the output state of the flip-flop 30, and switches to down-counting when the count value of the counter 25 reaches the maximum value. Similarly,
When the count value becomes equal to the minimum value (corresponding to the negative maximum amplitude value of the carrier wave), the mosquito small value discrimination circuit 28 outputs an underflow pulse (d). When the counter 25 receives an underflow pulse (d), it switches from down counting to up counting. The counter 25 repeats this operation and outputs a triangular waveform count fi (C) that changes between the maximum value and the minimum value. Count value (C
) into an analog quantity by the D/A converter 26, a carrier wave signal T as shown in FIG. 2 is obtained. On the other hand, the output signal (f) of the OR circuit 29 is generated when the carrier signal QT has the maximum positive and negative amplitude values. This signal (f) is given to the microcomputer 9 as a current detection timing signal CDT.

A PWM signal PWM for one phase is obtained by comparing the magnitude of the instantaneous voltage waveform signal v1'' obtained in the above manner with the carrier wave number T using a comparator 16. p
The number wMm is determined by comparing the instantaneous voltage modified signals of each phase whose phases are shifted by 120 degrees with the same carrier wave signal T.

In this embodiment, the carrier wave frequency is equal to the instantaneous voltage signals vi (
It is constant regardless of the frequency of the modulated wave signal M), and the modulated wave signal M and the carrier wave signal T are not synchronized.

Next, the control processing contents of the microcomputer 9 will be explained using FIG. 4.

The embodiment shown in Figure 1 separates the radio waves flowing through the induction motor into a component parallel to the rotating magnetic flux of the induction motor (wJ magnetic current component) and a component perpendicular to it (torque current component), and controls each component independently. This makes it possible to achieve island response control comparable to direct current. The microcomputer 9 performs such control processing by software processing, and FIG. 4 shows the details of the processing in an analog circuit format for ease of understanding. The broken line 9 in FIG. 4 represents the processing contents of the microcomputer. Microcomputer 9 is activated at regular intervals (approximately every 10m5)
The speed control task is activated by the timer interrupt to perform speed control processing, and the voltage VL detection task is activated by the interrupt pulse C1) T at each large amplitude moment of the carrier wave signal T (approximately every 1 mS) to perform current detection. processing and current control processing. Each process will be explained below.

First, in the speed control task, the count value of the output pulses of the rotary encoder is read from the counter 8, and the speed calculation means 38 calculates the speed from the count value.
, calculate. The microcomputer 9 stores this value in memory. Next, the speed command value f, * is set to the speed command setting circuit 13.
1 and store it in the capture memory. The difference between the speed detection value f successively received from the memory and each speed command value f is calculated, and speed control processing 39 is executed. From this, the command value I- for the torque llL flow is obtained, and this value is stored in the memory. Also,
The excitation current command value I+m' from the excitation current command circuit 132
Capture and store in memory. The command value f of the slip frequency and the tree are calculated from the command values ■, * of the nine torque currents stored in the memory and the command one shift ■- of the excitation l1Ik% flow. The frequency command value f+ of the voltage to be applied to the induction xm machine 6 is determined by adding this slip frequency command value f, * and the speed detection clay weight. This value is stored in memory and the speed control process ends.

Similarly, the speed control processing is performed at the next speed control 141 interrupt or pulse.

On the other hand, the current detection process and the 'lILm control process are performed as follows using the storm wave detection interrupt pulse CDT at each maximum amplitude point of the carrier wave T. 1. When the current detection section 1 current pulse CDT is input from the carrier wave signal generation circuit 15, the 5th
As shown in the figure, a selection signal for selecting the U-phase current among the U-phase, ■-phase, and W-phase currents is sent to the multiplexer 11, and at the same time a start signal is sent to the A/D converter 12. Accordingly, the multiplexer 11 applies the U-phase current detection section 1 of the current detector 10 to the A/D converter. A/D transformer 1
z converts the detected current value (analog value) into a digital value. The time required for the A/Di frame 12 to convert (approximately 20 μs
), the microcomputer 9 is forced to wait. After the conversion is completed, the microcomputer 9 transfers the digital U-phase current value to the A/D converter 1.
2 and store it in the capture memory. Next, a selection signal and a start signal for detecting the phase II current are sent to the multiplexer 11 and the A/D converter 12, and the digital amount of the phase phase current (*1) is detected using the same process as for the U phase. Take in and store this value in the memory.Similarly, take in the W phase current blood and store in the memory.The operating waveform at this time is the fifth waveform.
It will look like the figure. The three-phase instantaneous current values 11, 1v11. obtained by detection in this way. , the current component calculation means 4
1, torque 'current component 1, - and excitation current component 1m
a and store its value in memory. Next, the torque current command value ■- and the excitation current command value Is'' stored through the speed control process described above are read out from the memory, and the torque current component Ita obtained through the current detection process and the excitation current 'vIL' are read out from the memory.
The current control means 4 calculates the polarization of the current component 11 and the current component 11 respectively.
Give 2°43. Command value V of the torque direction component of the voltage applied to the induction motor 6 by the torque current control means 43
- is obtained, and the excitation current control means 42 obtains the command value V,'' of the excitation direction component.When these calculations are completed, the microcomputer calculates the frequency determined by the speed control process described above and stored in the memory. Command f*ft” and voltage command value V −, V
m" as a command to the instantaneous voltage generation circuit 14. As a result, a sinusoidal instantaneous voltage waveform corresponding to the command is obtained. This completes the processing for each current detection interrupt, and the next current detection interrupt Perform similar processing.

If the processing contents of the microcomputer described above are shown in flowcharts, the speed control task will be as shown in FIG. 6, and the current detection task will be as shown in FIG. 7.

Next, the PWM generated by the control processing described above
Figure i48 shows the relationship between the PWM signal and the current output from PWM inverter 1 to the induction motor. I will explain from C. First, change tA for three phases given as instantaneous voltage waveform for three phases.
The relationship between the wave polarization M, , M, , M and the carrier signal T is the eighth
The result will be as shown in Figure (a). Note that the figure shows a case in which variable all wave signal M and carrier wave m T are synchronized for easy understanding. Modulated wave signals of each phase M, , M, , M
, and the carrier wave signal T.
The phase voltages e*, e-, and ew of each phase output from the PWM inverter according to the signals are as shown in Fig. 8(b), (C),
(d). At this time, the line voltage e1 of the U phase-■ correlation. is as shown in the same figure (e). -The output current from the PWM inverter 1 to the induction motor 6 flows according to each phase voltage on the load side. Now, the load side phase voltage v of U phase
, N are expressed as follows using the phase voltages es + ew + ew of each phase.

Here, N represents the neutral point on the load side. From this relationship,
The waveforms of voltages v and N are expressed as shown in FIG. 8(f).

Therefore, the U-phase electric current fii, l flowing through the induction motor 6
pulsates in response to fluctuations in the voltages v and N, resulting in a waveform as shown in (2) in the figure. At this time, the fundamental wave component of current i lags behind the fundamental wave component of voltage v, N by a phase amount corresponding to the impedance of the induction motor 6. The pulsating U-phase current 1 is expressed as a carrier wave signal. If detected at each maximum amplitude point of T, the obtained horizontal value will be as shown by the black circle in the same figure (h).In other words, at the negative maximum amplitude point 1 of the carrier signal T, the instantaneous current of the phase current is detected. When it is detected, the detection timing is as shown in the figure (-), and the first detection Ip is obtained. Even at the positive maximum amplitude time tQ of the carrier wave signal T, the horizontal output value IQ is obtained at the same timing. The waveform connected by a smooth curve is shown by the broken line in Fig. 9(h).Now, if we examine the relationship between the pulsating current waveform and the t-current detection timing in detail, it becomes as shown in Fig. 9. Figure 9 (
(a) shows the current detection tying signal CDT that coincides with the maximum amplitude point of the carrier signal, (b) shows the relationship between the U-phase modulation temporary polarization M8 and the carrier signal T, and (C) shows the U-phase load-side phase voltage vaN.
, and (d) is the U phase ' flowing through voltage v and N.
Turtle style! , is the waveform of . As is clear from the figure, the voltage vm
N! Intersection point A, t of #4 wave signal and carrier wave No. 13 T
It is switched at the time 10, and accordingly the U-phase current i also pulsates. Since the frequency of the carrier wave signal T is sufficiently different from the modulated wave signal M, the modulated wave J@ No. Mu does not change too rapidly with respect to the carrier wave. In addition, carrier wave No. 16 T
has a triangular waveform. Therefore, the time tQ of the maximum amplitude point Q of the carrier wave signal T, which is the current detection point, corresponds to approximately the midpoint of the two intersection points A and B where the modulated wave signal M1 and the carrier wave signal T intersect. . As a result, the current value Io detected at the maximum amplitude time point tQ of the carrier wave signal T represents approximately the average value of the currents Ii and in at the peak time of pulsation. Therefore, the current value detected at this timing means that the fundamental wave component is detected. This corresponds to the curve shown by the broken line in FIG. 8(h).

As described above, according to the present invention, the current detection value of the fundamental wave component of the output current can be obtained without the influence of pulsation by discrete current detection every time near the maximum amplitude value of the carrier wave signal. Current control with good responsiveness can be realized by detecting the current flowing through the υ induction motor using such current detection and controlling the current. Furthermore, it is assumed that discrete processing is performed at each time point of maximum amplitude of the carrier wave, and is suitable for use in a digital control device using a microcomputer.

It should be noted that in the above embodiment, there is no need to generate a PWM signal! 1401. Although the case where the signal and the carrier signal are asynchronous has been described, the same relationship holds true even in the case of a synchronous method, so it can be applied.

Furthermore, it is of course possible to detect when the amplitude of either the positive or negative part of the carrier wave signal is at its maximum value.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the invention, Fig. 2 is a detailed block diagram of a part of Fig. 1, and Fig. 3 is an operation waveform diagram of generation of 9Ii wave signal current detection timing signal. , FIG. 4 is a block diagram illustrating the control processing contents of the microcomputer in FIG. 1 in analog form, FIG. 5 is a time chart for explaining the operation of current detection, and FIGS. FIG. 8 is a rounded operation waveform diagram illustrating the relationship between the carrier wave signal and the pulsating output current, and FIG. 9 is a partially enlarged waveform diagram of FIG. 8. 1...PWM inverter, 3...Forward converter, 5...
・Inverse converter, 6... Induction motor drive, 7... Rotary encoder, 9... Microcomputer, 10...
Current detector, 11...Multiplexer, 12...A
/D converter, 14... Instantaneous voltage waveform generation circuit, 15.
...Carrier signal generation circuit, M...Modulated wave signal, CDT
...Current detection L
J Mushroom 5 (2) No. 912]

Claims (1)

[Claims] 1. In a PWM converter whose ignition is controlled by a pulse signal obtained by comparing a triangular carrier wave signal with a modulated wave signal whose frequency and amplitude are proportional to the fundamental wave of the output voltage, the carrier wave signal is near the maximum amplitude value. PW which is a beast that detects the output current of the PWM converter when
How to detect the power supply of M-transformer.