CN102684535A - PWM (pulse-width modulation) method implemented by using fixed modulation ratio - Google Patents
PWM (pulse-width modulation) method implemented by using fixed modulation ratio Download PDFInfo
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- CN102684535A CN102684535A CN2012101197003A CN201210119700A CN102684535A CN 102684535 A CN102684535 A CN 102684535A CN 2012101197003 A CN2012101197003 A CN 2012101197003A CN 201210119700 A CN201210119700 A CN 201210119700A CN 102684535 A CN102684535 A CN 102684535A
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Abstract
The invention provides a PWM (pulse-width modulation) method implemented by using a fixed modulation ratio, which is characterized by comprising the following steps of: taking a controllable rectifying loop as the forestage circuit of an inverter; in the process of carrying out PWM, keeping the modulation depth constant; when the frequency is reduced, enabling the output direct-current-side voltage to be reduced through the controllable rectifying loop, so that the output voltage of the inverter is reduced; and when the frequency is increased, enabling the output direct-current-side voltage to be increased through the controllable rectifying loop, so that the output voltage of the inverter is increased, thereby achieving the purpose of changing the voltage while the frequency is changed. The method provided by the invention has the advantages that: the problem that the pulse width of the output voltage of the inverter is too narrow is improved, and the harmonic content under the condition of low frequencies can be effectively reduced.
Description
Technical field
The present invention relates to a kind of pulse duration modulation method of fixed modulation depth, relate in particular to the pulse duration modulation method of the adjustable RHVC of a kind of dc voltage, belong to the variable-frequency control technique field.
Background technology
Pulse-width modulation (PWM-Pulse Width Modulation) is to utilize the signal wave that is equivalent to fundametal compoment that triangular carrier is modulated, and reaches a kind of method of regulating output pulse width.
With the single-phase inverter is example, and its topological circuit is as shown in Figure 1, but but comprises keyholed back plate V1 to V1 and anti-and diode VD1 to VD4 anti-and on each keyholed back plate.At modulating wave is under the situation of sine wave; The fundamental voltage amplitude that adopts PWM to modulate the single-phase frequency converter output voltage that obtains is M*udc, and wherein, M is a modulation depth; Be the ratio of signal wave amplitude and triangular wave amplitude, the dc voltage of udc for obtaining through commutating circuit.But the PWM modulated waveform of keyholed back plate V1 is as shown in Figure 2.It is thus clear that output voltage amplitude is relevant with M and udc.
When frequency control, when adopting the variable voltage variable frequency mode, when frequency raises, the corresponding increase of voltage.Carry out PWM when modulation, common way is fixing direct voltage and change modulation depth M, thereby output voltage is changed.The modulation waveform of 50Hz (M=1) is shown in Fig. 2 A and Fig. 2 B, and the modulation waveform of 25Hz (M=0.5) is shown in Fig. 3 A and Fig. 3 B.Under this mode, M reduces along with modulation depth, and pulse duration also can reduce.Under low frequency, may be left in the basket because of pulse duration is narrow, thereby cause the distortion of output waveform; In addition, the content at the low frequency time-harmonic wave also can increase.
Summary of the invention
The purpose of this invention is to provide the PWM modulator approach that a kind of output voltage that under low frequency, makes inverter can not distort.
In order to achieve the above object, technical scheme of the present invention has provided a kind of PWM modulator approach of fixed modulation ratio, it is characterized in that; Step is: the front stage circuits of inverter adopts controlled commutating circuit; When carrying out the PWM modulation, keep modulation depth constant, when frequency reduces; Through controlled commutating circuit the dc voltage of output is reduced, thereby the output voltage of inverter is reduced; When frequency raises, through controlled commutating circuit dc voltage is increased, thereby the output voltage of inverter is increased, thereby reach the purpose of variable-frequency variable-voltage.
Dc voltage of the present invention is adjustable, therefore is particularly useful for the controlled frequency converter of rectification side.When carrying out the PWM modulation, modulation depth immobilizes, and then the width of the pulse voltage of output can not reduce because frequency is low, and pulse duration keeps higher level, and harmonic wave of output voltage content is significantly reduced.
Advantage of the present invention is: improve the narrow problem of frequency converter output voltage pulse duration, can effectively reduce the harmonic content under the low frequency simultaneously.
Description of drawings
Fig. 1 is the topological circuit of single-phase inverter;
Fig. 2 A is the PWM modulation signal figure of 50Hz;
Fig. 2 B is the output signal diagram of Fig. 2 A;
Fig. 3 A is the PWM modulation signal figure of 25Hz;
Fig. 3 B is the output signal diagram of Fig. 3 A;
Fig. 4 A is the PWM modulation signal figure of 25Hz of the present invention;
Fig. 4 B is the output signal diagram of Fig. 4 A.
Embodiment
For making the present invention more obviously understandable, now with a preferred embodiment, and conjunction with figs. elaborates as follows.
The PWM modulator approach of a kind of fixed modulation ratio provided by the invention the steps include: that the front stage circuits of inverter adopts controlled commutating circuit, and this arrangement loop can be the controlled three phase rectifier of thyristor loop.When carrying out the PWM modulation, keep modulation depth constant, in the present embodiment, fixed modulation depth M is 1.When frequency reduces, through controlled commutating circuit the dc voltage of output is reduced, promptly reduce the amplitude of dc voltage, thereby the output voltage of inverter is reduced; When frequency raises, through controlled commutating circuit dc voltage is increased, promptly increase the amplitude of dc voltage, thereby the output voltage of inverter is increased, thereby reach the purpose of variable-frequency variable-voltage.For the modulation waveform of 25Hz shown in Fig. 4 A and Fig. 4 B.
Through to Analysis of harmonic output voltage, the output harmonic wave of the PWM modulation system of fixed modulation depth provided by the invention is little more a lot of than the output harmonic wave of the PWM modulation system that changes modulation depth.Therefore, the present invention can effectively suppress the harmonic content under the low frequency, and the narrow problem of pulse width also can improve during simultaneously for low frequency.
Claims (1)
1. the PWM modulator approach of a fixed modulation ratio; It is characterized in that step is: the front stage circuits of inverter adopts controlled commutating circuit, when carrying out the PWM modulation; Keep modulation depth constant; When frequency reduces, through controlled commutating circuit the dc voltage of output is reduced, thereby the output voltage of inverter is reduced; When frequency raises, through controlled commutating circuit dc voltage is increased, thereby the output voltage of inverter is increased, thereby reach the purpose of variable-frequency variable-voltage.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2012101197003A CN102684535A (en) | 2012-04-22 | 2012-04-22 | PWM (pulse-width modulation) method implemented by using fixed modulation ratio |
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| CN2012101197003A CN102684535A (en) | 2012-04-22 | 2012-04-22 | PWM (pulse-width modulation) method implemented by using fixed modulation ratio |
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| CN2012101197003A Pending CN102684535A (en) | 2012-04-22 | 2012-04-22 | PWM (pulse-width modulation) method implemented by using fixed modulation ratio |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113489345A (en) * | 2021-05-17 | 2021-10-08 | 上海新时达电气股份有限公司 | Controllable rectifier control method, rectifier controller, frequency converter and storage medium |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2001016860A (en) * | 1999-06-24 | 2001-01-19 | Matsushita Electric Ind Co Ltd | Inverter controller |
| CN1281289A (en) * | 2000-06-07 | 2001-01-24 | 深圳市华为电气技术有限公司 | Method and device based on modulation percentage for controlling instantaneous value of pulse width modulated sine waves for inverter |
| JP2002101685A (en) * | 2000-09-25 | 2002-04-05 | Sanyo Electric Co Ltd | Inverter |
-
2012
- 2012-04-22 CN CN2012101197003A patent/CN102684535A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2001016860A (en) * | 1999-06-24 | 2001-01-19 | Matsushita Electric Ind Co Ltd | Inverter controller |
| CN1281289A (en) * | 2000-06-07 | 2001-01-24 | 深圳市华为电气技术有限公司 | Method and device based on modulation percentage for controlling instantaneous value of pulse width modulated sine waves for inverter |
| JP2002101685A (en) * | 2000-09-25 | 2002-04-05 | Sanyo Electric Co Ltd | Inverter |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113489345A (en) * | 2021-05-17 | 2021-10-08 | 上海新时达电气股份有限公司 | Controllable rectifier control method, rectifier controller, frequency converter and storage medium |
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Application publication date: 20120919 |