阅读说明：本技术 一种三相变频交流发电系统过压抑制装置分级卸载方法 (Grading unloading method for overvoltage suppression device of three-phase variable-frequency alternating-current power generation system ) 是由 姚贞羽 邵静 王智慧 于 2019-11-07 设计创作，主要内容包括：本发明提出一种三相变频交流发电系统过压抑制装置分级卸载方法,当检测到三相电压值经过过压抑制装置抑制达到给定值时,结合过电压抑制时功率回路的PWM占空比以及给定的卸载时间,进行分级卸载时PWM控制占空比的计算,并输出该占空比以实现过压抑制装置的分级卸载,从而将过压抑制装置中的抑制负载分成若干小载分步卸掉,可以有效保证抑制负载卸载时电网电压的平滑过渡,尽可能保证电网及后级用电设备的安全、可靠、稳定工作。(The invention provides a grading unloading method for an overvoltage suppression device of a three-phase variable-frequency alternating-current power generation system, which is characterized in that when a three-phase voltage value is detected to reach a given value through the suppression of the overvoltage suppression device, the PWM duty ratio of a power loop during overvoltage suppression and given unloading time are combined to calculate the PWM control duty ratio during grading unloading, and the duty ratio is output to realize grading unloading of the overvoltage suppression device, so that a suppression load in the overvoltage suppression device is divided into a plurality of small loads to be unloaded step by step, the smooth transition of the voltage of a power grid during load unloading can be effectively guaranteed, and the safe, reliable and stable operation of the power grid and rear-stage electric equipment can be guaranteed as far as possible.)

1. The grading unloading method of the overvoltage suppression device of the three-phase variable-frequency alternating-current power generation system is characterized by comprising the following steps of:

step 1: the method comprises the steps that a three-phase voltage sampling value is obtained by carrying out partial pressure and effective value calculation on a three-phase voltage output by a generator;

step 2: comparing the three-phase voltage sampling value obtained in the step (1) with a set threshold, if the three-phase voltage sampling value is greater than the set threshold, continuing overvoltage suppression, otherwise, entering the step (3);

and step 3: detecting the duty ratio delta of the input PWM control wave during overvoltage suppression, and calculating the grading number k and the corresponding different pulse width duty ratios p during grading unloading according to the following formula;

and 4, step 4: obtaining a PWM wave corresponding to each stage of unloading according to the pulse width duty ratio corresponding to each stage of unloading calculated in the step 3;

and 5: and (4) sequentially inputting the PWM wave corresponding to each stage of unloading obtained in the step (4) into an IGBT driving circuit of the PWM control energy absorption power loop according to a grading sequence, and driving the IGBT module to realize grading unloading of the power suppression load.

2. The grading unloading method for the overvoltage suppression device of the three-phase variable-frequency alternating-current power generation system according to claim 1, wherein the energy absorption power loop comprises a full-bridge rectification circuit of three-phase voltage, a support capacitor, an IGBT module, a freewheeling diode and an absorption capacitor; under the control of different duty ratios, the energy absorption loop realizes the rectification of three-phase alternating-current voltage through full-bridge rectification; the output voltage of the full-bridge rectification is further smoothed by the support capacitor; and absorbing the peak voltage generated when each PWM is turned off through an absorption capacitor connected in parallel at the output end of the IGBT module.

Technical Field

The invention belongs to the field of aviation variable-frequency alternating-current power generation systems, and relates to a grading unloading technology for a transient overvoltage dynamic suppression device of a three-level variable-frequency generator.

Background

When a high-power variable-frequency alternating-current power generation system performs high-capacity load switching or fails, due to control protection delay of a generator controller, inherent response time of a contactor and residual magnetism inside a main generator when the contactor is disconnected, the output end of the generator generates serious overvoltage, and system protection is interrupted or rear-stage electric equipment fails. When overvoltage occurs, the overvoltage suppression device of the three-phase variable-frequency alternating-current power generation system is matched with the generator controller, the generator controller cuts off excitation voltage, energy generated by residual excitation of the main generator is effectively absorbed by putting a suppression load into the transient overvoltage suppression device, power supply system error protection caused by overvoltage can be effectively prevented, and damage of high voltage to rear-stage electric equipment is avoided.

Disclosure of Invention

The invention provides a grading unloading technology of a power suppression load, which aims at the harm to a power grid caused by sudden unloading of the power suppression load directly after an overvoltage suppression device of a three-phase variable-frequency alternating-current power generation system completes effective suppression of overvoltage. Through the graded unloading of the restraining load, the smooth transition of the voltage of the power grid can be realized when the overvoltage restraining device is withdrawn for use, the safe, reliable and stable work of the power grid and the post-stage electric equipment is ensured as far as possible, and the robustness of the power supply system is improved.

The technical scheme of the invention is as follows:

the grading unloading method of the overvoltage suppression device of the three-phase variable-frequency alternating-current power generation system comprises the following steps of:

step 1: the method comprises the steps that a three-phase voltage sampling value is obtained by carrying out partial pressure and effective value calculation on a three-phase voltage output by a generator;

step 2: comparing the three-phase voltage sampling value obtained in the step (1) with a set threshold, if the three-phase voltage sampling value is greater than the set threshold, continuing overvoltage suppression, otherwise, entering the step (3);

and step 3: detecting the duty ratio delta of the input PWM control wave during overvoltage suppression, and calculating the grading number k and the corresponding different pulse width duty ratios p during grading unloading according to the following formula;

and 4, step 4: obtaining a PWM wave corresponding to each stage of unloading according to the pulse width duty ratio corresponding to each stage of unloading calculated in the step 3;

and 5: and (4) sequentially inputting the PWM wave corresponding to each stage of unloading obtained in the step (4) into an IGBT driving circuit of the PWM control energy absorption power loop according to a grading sequence, and driving the IGBT module to realize grading unloading of the power suppression load.

Furthermore, the energy absorption power circuit comprises a full-bridge rectification circuit of three-phase voltage, a support capacitor, an IGBT module, a freewheeling diode and an absorption capacitor; under the control of different duty ratios, the energy absorption loop realizes the rectification of three-phase alternating-current voltage through full-bridge rectification; the output voltage of the full-bridge rectification is further smoothed by the support capacitor; and absorbing the peak voltage generated when each PWM is turned off through an absorption capacitor connected in parallel at the output end of the IGBT module.

Advantageous effects

The invention can effectively ensure the smooth transition of the voltage of the power grid when the overvoltage suppression device suppresses the load unloading through the grading unloading mode of the overvoltage suppression device, and ensure the safe, reliable and stable work of the power grid and the post-stage electric equipment as far as possible.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1: a step unloading functional block diagram of the overvoltage suppression device;

FIG. 2: and a step unloading architecture block diagram of the overvoltage suppression device.

Detailed Description

According to the invention, when a variable-frequency alternating-current generator controller suddenly unloads a small load, the current change of a load end is small, and the caused voltage sudden-rise amplitude is also low (relative to the sudden-unloading of a large load), the restraining load in the over-voltage restraining device is divided into a plurality of small loads to be unloaded step by controlling the PWM duty ratio, so that the smooth transition of the power grid voltage during the unloading of the restraining load can be effectively ensured.

And when the three-phase voltage value is detected to reach a given value through the overvoltage suppression device, the PWM duty ratio of the power loop during overvoltage suppression and the given unloading time are combined to calculate the PWM control duty ratio during graded unloading, and the duty ratio is output to realize graded unloading of the overvoltage suppression device.

The grading unloading process of the overvoltage suppression device of the three-phase variable-frequency alternating-current power generation system comprises the following steps:

step 1: the method comprises the steps that a three-phase voltage sampling value is obtained by carrying out partial pressure and effective value calculation on a three-phase voltage output by a generator;

step 2: comparing the three-phase voltage sampling value obtained in the step (1) with a set threshold, if the three-phase voltage sampling value is greater than the set threshold, continuing overvoltage suppression, otherwise, entering the step (3);

and step 3: detecting the duty ratio delta of the input PWM control wave during overvoltage suppression, and calculating the grading number k and the corresponding different pulse width duty ratios p during grading unloading according to the following formula;

when the duty ratio delta is larger than or equal to 0.7, the grading number k is 3, the pulse width duty ratio p1 corresponding to the first-stage unloading is 70%, the pulse width duty ratio p2 corresponding to the second-stage unloading is 40%, and the pulse width duty ratio p3 corresponding to the third-stage unloading is 0; when the duty ratio is more than or equal to 0.3 and less than or equal to δ and less than 0.7, the grading number k is 2, the pulse width duty ratio p1 corresponding to the first-stage unloading is δ/2, and the pulse width duty ratio p2 corresponding to the second-stage unloading is 0; when the duty cycle δ is <0.3, no classification is made;

and 4, step 4: obtaining a PWM wave corresponding to each stage of unloading according to the pulse width duty ratio corresponding to each stage of unloading calculated in the step 3;

and 5: and (4) sequentially inputting the PWM wave corresponding to each stage of unloading obtained in the step (4) into an IGBT driving circuit of the PWM control energy absorption power loop according to a grading sequence, and driving the IGBT module to realize grading unloading of the power suppression load.

A schematic block diagram of the staged unloading of the overvoltage suppression device is shown in fig. 1. Providing an input [3] for three-phase voltage sampling through the three-phase voltage division [1] and the effective value calculation [2 ]; determining whether to enter the grading unloading of the overvoltage suppression device or continue the overvoltage suppression through the voltage judgment [4 ]; and (3) detecting the duty ratio of the PWM control wave during power absorption [5] and calculating the grading number and the corresponding different pulse width duty ratios during grading unloading by combining the unloading time given by the grading unloading. The larger the PWM duty ratio put into power absorption, the larger the number of stages. And the IGBT drive [8] provides the drive power required by the normal operation of the IGBT for the energy absorption loop. The energy absorption power loop [9] comprises a full-bridge rectification circuit of three-phase voltage, a support capacitor, an IGBT module, a freewheeling diode, an absorption capacitor and the like. Under the control of different duty ratios, the energy absorption loop [9] realizes the rectification of three-phase alternating-current voltage through full-bridge rectification; the output voltage of the full-bridge rectification is further smoothed by the support capacitor, so that the interference of alternating ripple waves is reduced; the absorption capacitor connected in parallel at the output end of the IGBT absorbs the peak voltage generated by stray inductance and the like when each PWM is turned off, so that the IGBT can work in a safe working range.

The overvoltage suppression device stage unloading architecture block diagram is shown in fig. 2, and an effective sampling input is provided through a voltage division circuit and an effective value calculation circuit. In the DSP processing circuit, after the high voltage is confirmed to be effectively inhibited, PWM with different duty ratios is output through the DSP to control the on and off of the IGBT of the power loop, so that the pulse width of the voltage on the inhibiting load is controlled to be gradually reduced from high, and the grading unloading of the overvoltage inhibiting device is realized.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made in the above embodiments by those of ordinary skill in the art without departing from the principle and spirit of the present invention.