JPH0442780A - Pwm controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a PWM control device that controls on/off a self-exciting converter for grid connection.

(Prior art) This type of PWM control device has a PWM control device as shown in FIG.
A sine wave as a WM reference wave signal and a triangular wave as a PWM carrier signal are compared, and the PWM reference wave signal level is P
Generates a pseudo sine wave signal that reaches the rHJ level during a period when it is higher than the WM carrier signal level and reaches the rLJ level during other periods, and controls the self-excited converter on and off in response to the level of this pseudo sine wave signal. are doing.

In this case, by matching the zero-crossing point of the PWM reference wave signal and the zero-crossing point of the PWM carrier signal, the positive side waveform and negative side waveform of the pseudo sine wave signal match, and the electrical angle The left-right symmetry of the waveform seen in the 180-degree interval is also ensured.

In this way, P
Synchronous PWM is a control method that shifts the phase of the WM carrier signal.
It is called. In order to realize synchronous PWM, conventionally, the active power P1 to be supplied to the grid, the reactive power Q, and the grid voltage vs.
d and the phase difference φ between the converter output voltage and the grid voltage
There is a method of detecting the phase difference φ and shifting the phase of the PWM carrier signal by this phase difference φ.

・In other words, the grid voltage is ■sd, the active power supplied to the interconnected grid is P1, the reactive power is Q1, the grid interconnection reactance is
1 converter drive voltage to V. Then, active power P and reactive power Q are expressed by the following equations.

From equations (1) and (2), φ is calculated using the following equation.

However, voxvsdXcO8φ The value of φ shifts the phase of the PWM reference wave and the PWM carrier wave. Note that the modulation rate of the PWM reference wave is determined by equation (4).

(Problem to be Solved by the Invention) The above-mentioned synchronous PWM calculates the phase difference φ between the converter output voltage and the grid voltage using the arctangent value according to equation (3). However, this method has a problem in that calculation accuracy and speed cannot be improved unless a table with a relatively large capacity is used.

In addition, it is generally difficult to shift the phase of the PWM carrier wave, and for this reason, the phase of the PWM carrier wave may not be aligned with the PWM reference wave, but if this is done, reactive power control,
There is a problem in that AC/DC conversion operations generate harmonics that adversely affect the grid.

This invention was made to solve the above problems, and it is possible to constantly match the phases of the PWM reference wave and the PWM carrier wave, thereby suppressing the amount of harmonics generated in the converter power. The purpose of the present invention is to obtain a PWM control device that can perform the following functions.

[Structure of the invention]

(Means for Solving the Problem) This invention generates a pseudo sine wave signal by comparing a PWM reference wave signal and a PWM carrier wave signal, and turns on a converter for grid connection by this pseudo sine wave signal. PW to control off
In the M control device, generating a reference wave signal for generating the PWM reference wave signal based on the detected system voltage, the output current of the converter, and the set active power output standard and reactive power output standard of the converter. a synchronizing signal generating means for generating a phase signal synchronized with the voltage of the system, inputting the phase signal, correcting it so as to be synchronized with the PWM reference wave signal, and generating a zero cross with the corrected phase signal. and carrier wave signal generation means for generating a PWM carrier wave signal with matching points.

(Function) In this invention, P is calculated based on the system voltage, the output current of the converter, the active power output standard, and the reactive power output standard.
While generating the WM reference wave signal, a phase signal synchronized with the grid voltage is generated, and a signal is created by correcting this phase signal so that it is synchronized with the PWM reference wave signal, and the zero cross point matches the corrected phase signal. Since the PWM carrier wave signal is generated, the phases of the PWM reference wave and the PWM carrier wave can be constantly matched, and thereby the amount of harmonics generated in the converter power can be suppressed.

(Embodiment) FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, the AC end of the self-excited converter 41 is connected to the primary side of the output transformer 42.
The secondary side of is connected to an AC system 50 via a circuit breaker 4B. Further, the DC end of the self-excited converter 41 is connected to the DC system 51.
It is connected to the. An instrument current transformer 44 and an instrument transformer 45 are provided between the output transformer 42 and the circuit breaker 46 which are interconnected in this way, and the active power detection circuit 22 detects the active power based on these output signals. The reactive power detection circuit 23 detects reactive power Pd and reactive power Q, respectively. Furthermore, the output current detection circuit 24 detects the output current 'sd of the self-exciting converter 41 based on the output of the instrument current transformer 44, and the system voltage detection circuit 25 detects the AC current based on the output of the instrument transformer 45. System voltage VSd+ is being detected.

On the other hand, the output signal of the potential transformer 45 is applied to the three-phase/two-phase conversion circuit 10. The three-phase/two-phase conversion circuit 10 converts the three-phase system voltage into a two-phase signal and applies the signal as one input to the phase difference detection circuit 11 . As the other input of the phase difference detection circuit 11, two phase signals read from the feedback signal generation circuit 6 and converted into analog quantities by the D/A converter 17 are added. The output of this phase difference detection circuit 11 is applied to a digital voltage controlled oscillator 13 via a loop filter 12, and a pulse having a frequency corresponding to the output of the phase difference detection circuit 11 is outputted from this digital voltage controlled oscillator 13. . And digital voltage controlled oscillator 13
The output pulses are counted by a phase counter 14, which outputs a digital phase signal θ. A counter reset circuit 15 is connected to the output circuit of this phase counter 14. And phase counter 1
When the count value of 4 reaches a value corresponding to one cycle of AC and overflows, the counter reset circuit 15 detects this and clears the phase counter 14. Note that the feedback signal generation circuit 16 includes a table from which two-phase data is read out according to changes in the phase signal θ.

The three-phase/two-phase conversion circuit 10 and the phase difference detection circuit 11 described here. loop filter] 2, digital voltage controlled oscillator 13, phase counter 14, counter reset circuit 15,
The feedback signal generation circuit 16 and the D/A converter 17 constitute a commercial synchronization circuit corresponding to the synchronization signal generation means of the present invention.

Further, a buffer 18 is provided to read the phase signal θ, and the phase signal θ temporarily stored in the buffer 18 is taken into the high-speed arithmetic circuit 26. The high-speed arithmetic circuit 26 includes an active power output standard P5 set by a setting device (not shown), a reactive power output standard Q, and an active power output value "sd' detected by the active power detection circuit 22". The reactive power output value Qsd detected by the output current detection circuit 24, the converter output current Sd detected by the output current detection circuit 24, and the grid voltage Vsd detected by the grid voltage detection circuit 25 are each A
/D converter 27.

As shown in detail in FIG. 2, this high-speed arithmetic circuit 26 includes subtraction means 61A, 61B, power/current reference conversion means 62, 3-phase/2-phase conversion means 63, d/q axis conversion means 64, and sine wave conversion means 61A, 61B. Signal generation means 65, subtraction means 66A.

66B, current/voltage conversion means 67. 2-phase AC conversion means 6
8. Consists of 2-phase/3-phase conversion means 69.

The buffer 18, high-speed arithmetic circuit 26, and A/D converter 27 described here constitute the reference wave signal generating means of the present invention.

On the other hand, the PWM reference wave signal output from the high-speed arithmetic circuit 26 is input to the PWM control circuit 40, where it is compared with the PWM carrier wave signal. At this time, the PWM reference wave signal is converted into 3-phase/2-phase by the sine wave generation circuit 30, and further converted into an analog signal by the D/A converter 31, and then added as one input of the phase difference detection port 32. It will be done. In addition,
The output of the phase difference detection circuit 32 is passed through a loop filter 33 and converted into a digital signal by an A7'D converter 34, and this digital data is input to a high-speed arithmetic circuit 26.

Then, the high-speed calculation circuit 26 sets the converted digital data in the phase setting circuit 35. Adder 3B adds this Δθ to the aforementioned phase signal θ and outputs a phase reference θ1. Based on this phase reference θ1, the sine wave generation circuit 37 generates a two-phase sine wave signal, similar to the feedback signal generation circuit 16 described above, and outputs it to the phase difference detection circuit 32 via the D/A converter 38. Add it as the other input. Further, the PWM carrier wave generation circuit 39 generates a PWM carrier wave signal based on the phase reference θ1 and applies it to the PWM control circuit 40.

These elements, namely the sine wave generation circuit 30, the D/A
Converter 31, phase difference detection circuit 32, loop filter 33
, A/D converter 34, phase setting circuit 35, adder 3B,
The sine wave generation circuit 37, the D/A converter 38, and the PWM carrier generation circuit 39 constitute carrier wave signal generation means of the present invention.

The operation of this embodiment configured as described above will be explained below.

First, the PWM control circuit 40 generates a pseudo sine wave signal,
The switching elements constituting the self-excited converter 41 are controlled to be turned on or off. As a result, active electric power and reactive power are supplied from the DC system 51 to the AC system 50. The active power detection circuit 22 detects this active power output value Pd, and the reactive power detection circuit 23 detects the reactive power output value P.sub.2.

Further, the output current detection circuit 24 detects the converter output current ■sd at this time, and the system voltage detection circuit 25 detects the system voltage v8d at this time.

Next, the three-phase/two-phase conversion circuit 10 receives the three-phase voltage signal 5100.
is a two-phase voltage signal, that is, 5 inches (ω is 10φ),
cos (ω = 10φ) is generated and applied to the phase difference detection circuit H. On the other hand, the feedback signal generation circuit 16 is 5 inches (ωt+θ
) and a feedback signal 5103 of cos (ωt+θ) are generated and applied to the phase difference detection circuit 11 via the D/A converter 17. The phase difference detection circuit 11 performs the following calculations based on these signals to determine the phase difference between the two-phase converted signal and the feedback signal.

5in (ωt + φ)・C05 (ω is 10) cos (ωt
+φ) -5in (ω is 10) -5in (φ-θ)
(5) Subsequently, the harmonic components in this phase difference signal 5 inches (φ-θ) are removed by the loop filter 12, and the digital voltage controlled oscillator 13
added to. This digital voltage controlled oscillator 1B generates a pulse signal 8104 that makes the phase difference signal 5in (φ-θ) zero by a feedback effect. This pulse signal 5104 is counted by phase counter I4. In this case, the count amount of the phase counter 14 is the specified value, that is,
When a value corresponding to one cycle of alternating current is reached, an overflow occurs, and at this time, the counter reset circuit 5 generates a clear signal 810B and adds it to the phase counter 14.

Note that the count amount of the phase counter 14 and the feedback signal generation circuit 1
The phase counter I4 is interlocked with the output signal phase of I4.
The timing of clearing is sinθ-0゜eOsθ=1
The table is set up so that

As a result, the phase counter 4 outputs a digital phase signal θ synchronized with the grid voltage.

Next, the high-speed calculation circuit 26 is connected to the active power detection circuit 22 described above.
, the outputs of the reactive power detection circuit 23, the output current detection circuit 24, the grid voltage detection circuit 25, and the output of a power standard setter (not shown) are inputted via the A/D converter 27, and the buffer 18, the phase signal θ is input, and the three-phase PW is controlled using the well-known ci-q control method on the rotating coordinate axis.
Generate M reference signal 5ilo.

In this case, as shown in FIG. 2, the active power output value P is subtracted from the active power output reference P by the subtraction means 61A to obtain the active power reference value P*, and the reactive power output is similarly obtained from the reactive power output reference Q. The reactive power reference value Q is obtained by subtracting the value Q.
Find *. The power/current reference conversion means 62 inputs the active power reference value P*, the reactive power reference value Q*, and the grid voltage detection detection value V, and calculates the converter current reference I by calculating the following equation.

On the other hand, the three-phase/two-phase conversion means 63 converter output current ISd
is input, converted into a two-phase signal, and output. d/q
The axis conversion means 64 converts the two-phase phase from the stationary coordinate axis to a value on the d-q axis rotating with the system frequency based on the sine component and eOs component of the rotating coordinate signal generated by the sine wave signal generation means 65. and add it as a feedback signal. The subtraction means 86A, 66B are connected to the converter current reference I1. The deviation between Id and this feedback signal is taken out and added to the current/voltage conversion means 67. The current/voltage conversion means 67 converts this deviation into a voltage signal V9. Convert to Vd.

The two-phase AC conversion means 68 converts the voltage signal (1) based on the rotational coordinate signal of the sine wave signal generation means 65. (2) Outputs the sine component and eO9 component of the AC signal on the stationary coordinate axis. The two-phase/three-phase conversion means 69 converts this sine component and CO
A PWM reference wave signal 5110 is output from the S component.

Next, the phase of this PWM reference wave signal 5110 is
In order to match the phase of the PWM carrier signal output by the carrier wave generation circuit 39, a PLL loop is used here for tracking. Here, as shown in equations (1), (2), and (3), in grid interconnection control that supplies active power and reactive power to the grid, the active power and reactive power are set to a predetermined value with respect to the grid voltage. It is given as a vector quantity with a phase shift, that is, a quantity having a sine component and a COS component.

Since the PWM carrier wave (vector amount) is made to match this vector amount, the sine component and COS component for the PWM carrier wave are generated based on the phase signal of the phase counter 14, and control is performed so that the inner product of the two vectors becomes 0. do.

Therefore, the sine wave generation circuit 30 inputs the reference wave signal 5110 and generates a two-phase alternating current similar to that obtained in the process of generating this reference wave signal 5110, that is, a sine component and a C
Output OS components. The D/A converter 31 converts this into an analog quantity and supplies it to the phase difference detection circuit 32. On the other hand, an adder 36 adds the phase signal output from the phase counter 14 and the phase difference signal Δθ set by the phase setting circuit 35, and outputs a phase reference θ1. Sine wave generation circuit 37
generates and outputs a sine component and an eO9 component using this phase reference θ1.

The D/A converter 38 converts this into an analog signal and provides it to the phase difference detection circuit 32. The phase difference detection circuit 32 is (5)
The equation is calculated and a phase difference signal is output. This phase difference signal is smoothed by the loop filter 33, and further, the A/D
The converter 34 converts it into a digital signal and outputs phase difference data 5130. Then, this phase difference data is set in the phase setting circuit 35, and control is actually performed to make this phase difference data zero.

As a result, the phase reference θ* output by the adder 36 is PW
The PWM carrier wave signal 51 is a signal synchronized with the M reference wave signal 5110 and is output from the PWM carrier generation circuit 39.
20 is synchronized with the PWM reference wave signal 511O, and the zero cross points of both coincide.

Therefore, in this embodiment, self-excited conversion that generates a small amount of harmonics can be connected to the grid.

In addition, in this embodiment, since the inner product of the two vectors is controlled to be zero, it does not depend on the magnitude of both vectors, and therefore, the PWM reference wave does not depend on the magnitude of the PWM reference wave. This has the effect that the phase of the PWM carrier wave can be matched with the PWM carrier wave.

Furthermore, in this embodiment, the high-speed arithmetic circuit 26
is the phase difference data 513 between the PWM reference wave and the PWM carrier wave.
Since 0 is read, the high-speed arithmetic circuit 26 can monitor the control state, that is, confirm whether the control is normal or abnormal.

In each of the above embodiments, a PLL circuit is used to
The phases of the WM reference wave and the PWM carrier wave are matched, and this can also be processed by software. That is, the sine wave generating circuit 30 to D/A converter 38 in FIG.
may be processed by software, and the PWM carrier wave may be generated by the PWM carrier generation circuit 39 based on the result.

Further, Δθ may be determined not by PLL processing but by a value determined by control calculation in the high-speed calculation circuit 26. That is, the PWM standard technique signal is originally a vector quantity, and the following two components V1 and Vd are obtained in dq control on the rotating coordinate axis. From these two quantities, the phase difference with the system voltage V8d is φ-jan""' (V / V) ・(8)
It is determined as Vd. In this case, it is sufficient to prepare a table for obtaining φ from the value of tanφ with desired accuracy.

Each of these methods provides current minor loop control, resulting in rapid phase alignment.

〔Effect of the invention〕

As is clear from the above explanation, according to this invention,
Since the PWM carrier signal whose zero cross point coincides with the PWM reference wave signal is generated, it is possible to reliably suppress the amount of harmonics generated in the converter power.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a block diagram showing the detailed configuration of the main elements of the same embodiment, and FIG. 3 is a diagram showing the principle of generating a PWM control signal. IO...3-phase/2-phase conversion circuit, 11.32... Phase difference detection circuit, 12... Loop filter, 13... Digital voltage controlled oscillator, 13... Phase counter, 1
5...Counter reset circuit, te...Feedback signal generation circuit, 17.31.38...D/A converter, 26.
・・High-speed arithmetic circuit, 27.34 ・・A/D converter, 3
0.37... Sine wave generation circuit, 33... Loop filter, 35... Phase setting circuit, 36... Adder, 39
. . . PWM carrier wave generation circuit, 40 . . . PWM control circuit, 41 . . . Self-excited converter.

Claims (1)

[Claims] In a PWM control device that compares a PWM reference wave signal and a PWM carrier wave signal to generate a pseudo sine wave signal, and controls a converter for grid connection on and off using this pseudo sine wave signal, the detected grid voltage and a reference wave signal generating means that generates the PWM reference wave signal based on the output current of the converter and set active power output standards and reactive power output standards of the converter, and a synchronization signal generation means for generating a phase signal, inputting the phase signal, correcting it so as to be synchronized with the PWM reference wave signal, and generating a PWM carrier wave signal whose zero cross point coincides with the corrected phase signal; A PWM control device comprising carrier wave signal generation means.