CN115842482A - MMC full-power frequency converter capacitor voltage low-frequency ripple suppression method and device - Google Patents
MMC full-power frequency converter capacitor voltage low-frequency ripple suppression method and device Download PDFInfo
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Abstract
The embodiment of the application provides a method and a device for suppressing low-frequency ripple of capacitor voltage of an MMC full-power frequency converter, wherein the method comprises the following steps: when the variable-speed pumped storage unit is in a variable-frequency starting or braking working condition, when the output frequency of the MMC frequency converter is in a preset range, generating a first voltage modulation wave component according to a preset high-frequency zero-sequence voltage and the three-phase output voltage of the MMC frequency converter, and generating a second voltage modulation wave component according to a preset high-frequency bridge arm circulation current and the bridge arm circulation current of the MMC frequency converter; and generating a driving signal according to the first voltage modulation wave component and the second voltage modulation wave component. High-frequency zero-sequence voltage is injected into the three-phase output voltage, and high-frequency bridge arm circulating current is injected into the bridge arm circulating current, so that the capacitor voltage pulsation can be effectively inhibited.
Description
Technical Field
The embodiment of the application relates to the technical field of pumped storage, in particular to a method and a device for inhibiting low-frequency pulsation of capacitor voltage of an MMC full-power frequency converter.
Background
The variable-speed operation pumped storage unit can optimize the generating efficiency, the absorption power under the pumping working condition is adjustable, and the variable-speed operation pumped storage unit has wide application prospect. Fig. 1 shows a pumped storage variable speed unit based on a full-power frequency converter, wherein a generator motor is a variable speed motor, and a stator of the generator motor is connected to a power grid through the full-power frequency converter, so that flexible connection between the generator motor and the power grid is realized. When the rotating speed of the generator motor changes, the frequency of the stator voltage of the generator motor also changes, the power grid frequency is always stable power frequency, the full-power frequency converter is used for converting alternating current with the changed frequency at the stator end into power frequency alternating current acceptable by the power grid, and meanwhile active and reactive bidirectional transmission is achieved.
A Back-to-Back Modular Multilevel full-power frequency Converter (MMC) based on a half-bridge sub-module is a full-power frequency Converter with better performance, and when a variable-speed pumped storage unit is in a variable-frequency starting or braking working condition, the full-power frequency Converter side is required to output variable-frequency and variable-voltage alternating current, and the frequency range of the variable-frequency and variable-voltage alternating current is larger and is usually close to 0-power frequency (50 Hz). When the alternating current output side frequency of the MMC frequency converter is lower, the capacitor voltage of the submodule of the MMC frequency converter can generate the pulse of corresponding frequency, and the pulse amplitude is inversely proportional to the output frequency and the capacitance value and is directly proportional to the load current. Therefore, under the working condition of variable frequency starting or braking, how to effectively inhibit the capacitance voltage pulsation of the MMC frequency converter is a problem to be solved in the field.
Disclosure of Invention
In view of this, an embodiment of the present invention provides a method and a device for suppressing low-frequency ripple of a capacitor voltage of an MMC full-power frequency converter, which can effectively suppress the low-frequency ripple of the capacitor voltage.
Based on the above purpose, an embodiment of the present application provides a method for suppressing low-frequency ripple of a capacitor voltage of an MMC full-power frequency converter, including:
when the variable-speed pumped storage unit is in a variable-frequency starting or braking working condition, when the output frequency of the MMC frequency converter is in a preset range, generating a first voltage modulation wave component according to a preset high-frequency zero-sequence voltage and the three-phase output voltage of the MMC frequency converter, and generating a second voltage modulation wave component according to a preset high-frequency bridge arm circulation current and the bridge arm circulation current of the MMC frequency converter; the high-frequency zero-sequence voltage is determined according to the phase output voltage amplitude, the bus direct-current voltage, a preset margin coefficient and the rated working frequency of the MMC frequency converter; the high-frequency bridge arm circulating current is determined according to phase output current, the amplitude of the phase output voltage, bus direct-current voltage, the margin coefficient, the initial phase of fundamental voltage and the rated working frequency;
and generating a driving signal according to the first voltage modulation wave component and the second voltage modulation wave component.
Optionally, when the output frequency of the MMC frequency converter is in a predetermined range, a first voltage modulation wave component is generated according to a predetermined high-frequency zero-sequence voltage and a three-phase output voltage of the MMC frequency converter, including:
and when the output frequency is smaller than a preset first low-frequency threshold value, superposing the high-frequency zero-sequence voltage and the three-phase output voltage respectively to obtain the first voltage modulation wave component.
Optionally, when the output frequency of the MMC frequency converter is within a predetermined range, generating a second voltage modulation wave component according to a predetermined high-frequency bridge arm ring current and a predetermined bridge arm ring current of the MMC frequency converter, including:
and when the output frequency is smaller than a preset second low-frequency threshold, regulating the high-frequency bridge arm circulating current by using a preset controller according to the bridge arm circulating current to obtain a second voltage modulation wave component.
Optionally, when the output frequency of the MMC frequency converter is within a predetermined range, generating a second voltage modulation wave component according to a predetermined high-frequency bridge arm ring current and a predetermined bridge arm ring current of the MMC frequency converter, further comprising:
and when the output frequency is greater than the second low-frequency threshold and smaller than the first low-frequency threshold, attenuating the high-frequency bridge arm circulating current according to the output frequency, and adjusting the attenuated high-frequency bridge arm circulating current by using the controller according to the bridge arm circulating current to obtain the second voltage modulation wave component.
Optionally, attenuating the high-frequency bridge arm circulating current according to the output frequency includes:
determining an attenuation coefficient according to the output frequency;
and attenuating the high-frequency bridge arm circulating current according to the attenuation coefficient.
Optionally, the controller is a dual-proportion resonance controller; and after the high-frequency bridge arm circulation current is adjusted by using a preset controller according to the bridge arm circulation current, obtaining a second voltage modulation wave component, wherein the method comprises the following steps:
calculating the difference value between the high-frequency bridge arm circulation current and the bridge arm circulation current;
and inputting the difference value into the double-proportion resonance controller, and outputting the second voltage modulation wave component by the double-proportion resonance controller.
Optionally, the high-frequency zero-sequence voltage is determined according to a formula (20):
wherein M is the ratio of the amplitude of the phase output voltage to the half-bus DC voltage, U dc Is a DC bus voltage, K cm As a margin coefficient, ω cm Is an angular frequency determined from the nominal operating frequency.
Optionally, the high-frequency bridge arm loop current is determined according to formula (21):
wherein, theta x Initial phase of the output voltage for x-phase, i x X = a, b, c, ω, for the output current of the x-phase out Is the alternating current output angular frequency of the MMC frequency converter.
Optionally, the transfer function of the double-proportion resonance controller is as follows:
wherein, K p Is a proportional gain factor, K r Is the resonant gain coefficient, omega i To account for the resonance term bandwidth of the-3 dB requirement, s is the Laplace operator, ω out The AC output angular frequency of the MMC frequency converter is obtained.
The embodiment of the present application further provides a device for suppressing low-frequency ripple of a capacitor voltage of an MMC full-power frequency converter, including:
the modulation module is used for generating a first voltage modulation wave component according to a preset high-frequency zero-sequence voltage and a three-phase output voltage of the MMC frequency converter when the variable-speed pumped storage unit is in a variable-frequency starting or braking working condition and when the output frequency of the MMC frequency converter is in a preset range, and generating a second voltage modulation wave component according to a preset high-frequency bridge arm circulation current and a bridge arm circulation current of the MMC frequency converter; the high-frequency zero-sequence voltage is determined according to the phase output voltage amplitude, the bus direct-current voltage, a preset margin coefficient and the rated working frequency of the MMC frequency converter; the high-frequency bridge arm circulating current is determined according to phase output current, the amplitude of the phase output voltage, bus direct-current voltage, the margin coefficient, the initial phase of fundamental voltage and the rated working frequency;
and the driving module is used for generating a driving signal according to the first voltage modulation wave component and the second voltage modulation wave component.
As can be seen from the above, according to the method and the device for suppressing the low-frequency ripple of the capacitance voltage of the MMC full-power frequency converter provided in the embodiment of the present application, when the variable-speed pumped storage unit is in the variable-frequency starting or braking condition, and when the output frequency of the MMC frequency converter is low, a first voltage modulation wave component is generated according to the predetermined high-frequency zero-sequence voltage and the three-phase output voltage of the MMC frequency converter, and a second voltage modulation wave component is generated according to the predetermined high-frequency bridge arm ring current and the bridge arm ring current of the MMC frequency converter; and generating a driving signal according to the first voltage modulation wave component and the second voltage modulation wave component. By injecting high-frequency zero-sequence voltage into the three-phase output voltage and injecting high-frequency bridge arm circulating current into the bridge arm circulating current, the capacitor voltage pulsation can be effectively inhibited.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the description below are only the embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a grid-connected architecture of a variable speed unit according to an embodiment of the present application;
FIG. 2 is a schematic flow chart of a method according to an embodiment of the present application;
fig. 3 is a schematic view of a topological structure of an MMC frequency converter and its sub-modules according to an embodiment of the present application;
FIG. 4 is a schematic diagram of a control model according to an embodiment of the present application;
FIG. 5 is a schematic diagram of an enable signal according to an embodiment of the present application;
FIG. 6 is a diagram illustrating the relationship between the attenuation coefficient and the output frequency according to an embodiment of the present application;
FIG. 7 is a schematic diagram of a frequency characteristic of a dual-ratio resonant controller according to an embodiment of the present application;
FIG. 8 is a schematic diagram of a capacitor voltage simulation waveform according to an embodiment of the present application;
FIG. 9 is a block diagram of an apparatus according to an embodiment of the present application;
fig. 10 is a block diagram of an electronic device according to an embodiment of the present application.
Detailed Description
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
It should be noted that technical terms or scientific terms used in the embodiments of the present application should have a general meaning as understood by those having ordinary skill in the art to which the present disclosure belongs, unless otherwise defined. The use of "first," "second," and similar terms in the embodiments of the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that the element or item listed before the word covers the element or item listed after the word and its equivalents, but does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.
As shown in fig. 2, an embodiment of the present application provides a method for suppressing low-frequency ripple of a capacitance voltage of an MMC full-power frequency converter, which is applied to a back-to-back modular multilevel full-power frequency converter (hereinafter referred to as an MMC frequency converter) based on half-bridge sub-modules, and the method includes:
s201: under the working condition that the variable-speed pumped storage unit is in variable-frequency starting or braking, when the output frequency of the MMC frequency converter is in a preset range, generating a first voltage modulation wave component according to a preset high-frequency zero-sequence voltage and the three-phase output voltage of the MMC frequency converter, and generating a second voltage modulation wave component according to a preset high-frequency bridge arm circulating current and the bridge arm circulating current of the MMC frequency converter;
s202: a drive signal is generated from the first voltage modulated wave component and the second voltage modulated wave component.
As shown in fig. 1-3, in this embodiment, the stator end of the variable-speed pumped storage unit is connected to the power grid through an MMC frequency converter, and the stator end ac power is converted into power frequency ac power acceptable to the power grid by using the MMC frequency converter. The MMC frequency converter is a symmetrical structure formed by a plurality of sub-modules, the sub-modules adopt a half-bridge structure, and when the variable-speed pumped storage unit is in a variable-frequency starting or braking working condition and the output frequency of the MMC frequency converter is lower, the capacitor voltage of the sub-modules pulsates at corresponding frequency. In order to inhibit low-frequency pulsation of capacitance voltage, when the output frequency (the frequency of output voltage and output current) of the MMC frequency converter is detected to be in a preset range, a first voltage modulation wave component is generated according to pre-generated high-frequency zero-sequence voltage and three-phase output voltage of the MMC frequency converter, and a second voltage modulation wave component is generated according to pre-generated high-frequency bridge arm circulation current and bridge arm circulation current of the MMC frequency converter; and generating a driving signal for driving the MMC frequency converter side converter based on the first voltage modulation wave component and the second voltage modulation wave component. Therefore, when the output frequency of the MMC frequency converter is low, the low-frequency pulsation of the capacitor voltage can be effectively inhibited by injecting high-frequency zero-sequence voltage and high-frequency bridge arm circulating current, and the stability of the system is ensured.
In some embodiments, when the output frequency of the MMC frequency converter is in a predetermined range, generating a first voltage modulation wave component according to a predetermined high-frequency zero-sequence voltage and a three-phase output voltage of the MMC frequency converter includes:
and when the output frequency of the MMC frequency converter is smaller than a preset first low-frequency threshold value, superposing the high-frequency zero-sequence voltage and the three-phase output voltage respectively to obtain a first voltage modulation wave component. That is, when the output frequency of the MMC frequency converter is lower than the first low frequency threshold, the problem of capacitance voltage ripple is likely to occur, and the first voltage modulation wave component for suppressing the capacitance voltage ripple is obtained by injecting the generated high-frequency zero-sequence voltage into the three-phase output voltage.
In some embodiments, when the output frequency of the MMC frequency converter is in a predetermined range, generating the second voltage-modulated wave component according to a predetermined high-frequency bridge arm circulating current and a bridge arm circulating current of the MMC frequency converter includes:
when the output frequency is smaller than a preset second low-frequency threshold value, a preset controller is used for regulating the high-frequency bridge arm circulating current according to the bridge arm circulating current to obtain a second voltage modulation wave component; or,
and when the output frequency is greater than the second low-frequency threshold and less than the first low-frequency threshold, attenuating the high-frequency bridge arm circulating current according to the output frequency, and adjusting the attenuated high-frequency bridge arm circulating current by using the controller according to the bridge arm circulating current to obtain a second voltage modulation wave component.
In this embodiment, when the output frequency of the MMC frequency converter is lower than the second low-frequency threshold, the difference between the generated high-frequency bridge arm loop current and the real-time detected bridge arm loop current of the MMC frequency converter is input to the controller, and the controller outputs the second voltage modulation wave component for suppressing the capacitance voltage ripple. Wherein the second low frequency threshold is less than the first low frequency threshold. When the output frequency of the MMC frequency converter is between a second low-frequency threshold and a first low-frequency threshold, firstly attenuating the high-frequency bridge arm circulating current, then inputting the difference value between the attenuated high-frequency bridge arm circulating current and the bridge arm circulating current detected in real time into a controller, and outputting a second voltage modulation wave component for inhibiting the capacitor voltage pulsation by the controller.
In some modes, the first low-frequency threshold may control the timing of injecting the high-frequency zero-sequence voltage in the form of an enable signal, and the first low-frequency threshold and the second low-frequency threshold may control the timing of injecting the high-frequency bridge arm loop current in the form of an enable signal and an attenuation coefficient.
As shown in fig. 5 and equation (1), the enable signal Ena can be expressed as:
according to the formula (1), when the output frequency f of the MMC frequency converter out And when the voltage is more than or equal to 0 and less than or equal to the first low-frequency threshold, injecting high-frequency zero-sequence voltage into the three-phase output voltage. Alternatively, the first low frequency threshold may be set to 15Hz.
The attenuated signal K is shown in FIG. 6 and equation (2) ih Can be expressed as:
according to the formula (2), when the output frequency of the MMC frequency converter is greater than or equal to 0 and less than a second low-frequency threshold value, directly injecting high-frequency bridge arm circulation current into the bridge arm circulation current of the MMC frequency converter; when the output frequency is greater than or equal to the second low-frequency threshold and smaller than the first low-frequency threshold, injecting the high-frequency bridge arm circulating current into the bridge arm circulating current after being attenuated according to the attenuation coefficient; and when the output frequency is greater than the first low-frequency threshold value, the high-frequency bridge arm circulating current does not need to be injected. The attenuation coefficient is determined according to the output frequency, the attenuation coefficient and the output frequency are in a linear attenuation relation, and the high-frequency bridge arm circulating current is linearly reduced along with the increase of the output frequency. Alternatively, the second low frequency threshold may be set to 10Hz.
In some embodiments, the controller employs a dual proportional resonant controller; and after the high-frequency bridge arm circulation current is regulated by utilizing a preset controller according to the bridge arm circulation current, a second voltage modulation wave component is obtained, and the method comprises the following steps:
calculating the difference value of the high-frequency bridge arm circulation current and the bridge arm circulation current;
and inputting the difference value into a double-proportion resonance controller, and outputting a second modulation wave component by the double-proportion resonance controller.
In the embodiment, a double-proportion resonance controller is adopted to carry out accurate closed-loop control on the high-frequency bridge arm circulating current. When the output frequency of the MMC frequency converter is lower than a second low-frequency threshold value, calculating a difference value between the high-frequency bridge arm circulating current and the actual bridge arm circulating current of the frequency converter, inputting the difference value into a double-proportion resonance controller, and outputting a corresponding second voltage modulation wave component by the double-proportion resonance controller; and when the output frequency is between the second low-frequency threshold and the first low-frequency threshold, calculating a difference value between the attenuated high-frequency bridge arm circulating current and the actual bridge arm circulating current, inputting the difference value into the double-proportion resonance controller, and outputting a corresponding second voltage modulation wave component by the double-proportion resonance controller.
The high-frequency bridge arm circulation has an output fundamental frequency component i x And a high frequency component sin (ω) cm t), and therefore ω exists in the high frequency arm loop current cm ±ω out Two main frequency components. As shown in fig. 7, the dual-ratio resonant controller can provide higher gain at two frequency points, and can realize accurate tracking of two frequency components.
In some embodiments, the transfer function of the dual-ratio resonant controller in the s-domain is:
wherein, K p Is a proportional gain factor, K r Is the resonant gain coefficient, omega i To account for the resonance term bandwidth of the-3 dB requirement, s is the Laplace operator, ω cm At angular frequency, omega, of high-frequency bridge arm circulation out The output angular frequency of the MMC frequency converter.
The following describes a method for determining high-frequency zero-sequence voltage and high-frequency bridge arm circulating current in detail with reference to specific embodiments.
Combining the circuit topology diagram of the MMC full-power frequency converter shown in FIG. 3, the DC bus voltage is U dc SM is a cascaded half-bridge submodule, L 0 Is bridge arm inductance, R 0 Is equivalent series resistance of a bridge arm. The midpoint voltage of the a, b, c three-phase voltage output end of the MMC frequency converter to the direct current bus is u x (x = a, b, c), expressed as:
wherein, U x The output voltage amplitude of the x phase is, and theta is the initial phase.
The output current of the MMC frequency converter is i x Expressed as:
wherein, I x The amplitude of the output current for the x-phase.
Defining the sum of the port voltages of all the submodules of the upper bridge arm as u px The sum of the port voltages of all the submodules of the lower bridge arm is u nx Neglecting the voltage drop on the bridge arm inductance to obtain:
defining the upper bridge arm current as i px The lower bridge arm current is i nx The current flowing through the upper and lower bridge arms in the same phase is bridge arm circulation current i zx Then, there are:
according to the input and output instantaneous power balance of each phase of the MMC frequency converter, the bridge arm circulation can be further represented as:
i zx ＝u x i x /u dc (8)
according to kirchhoff's current law, the output current of each phase can also be obtained from the difference between the currents of the upper and lower bridge arms, and is expressed as:
i x ＝i px -i nx (9)
high-frequency zero-sequence voltage u cm Superposing the three-phase output voltage of the MMC frequency converter to make a high-frequency bridge arm circulating current i cmx Injection of xThe frequency of the bridge arm circulation of the phase, the high-frequency zero-sequence voltage and the high-frequency bridge arm circulation are f cm Angular frequencies are all omega cm And obtaining bridge arm voltage as follows:
the upper and lower bridge arm currents are:
the instantaneous power of the upper bridge arm is the product of the bridge arm voltage and the bridge arm circulating current, and is expressed as:
p px ＝u px i px ＝(U dc /2-u x -u cm )(i zx +i x /2+i cmx )＝p x_cm +p x_dm (12)
the instantaneous power of the lower bridge arm is the product of the bridge arm voltage and the bridge arm circulating current, and is expressed as:
p nx ＝u nx i nx ＝(U dc /2+u x +u cm )(i zx -i x /2+i cmx )＝p x_cm -p x_dm (13)
wherein,
p contained in the instantaneous power of the upper and lower arms according to equation (14) x_cm Item, item one
High-frequency bridge arm circulating current i containing high-frequency component cmx The second term->
High-frequency zero-sequence voltage u containing high-frequency components cm . P contained in the instantaneous power of the upper and lower arms according to equation (15) x_dm Of the terms, the first term is a low-frequency component, and the second term u cm i cmx High-frequency bridge arm circulating current i containing high-frequency component cmx And high frequency zero sequence voltage u cm Item u, item three x i cmx High-frequency bridge arm circulating current i containing high-frequency component cmx The fourth term->
High-frequency zero-sequence voltage u containing high-frequency components cm . For the low-frequency component of the instantaneous power of the bridge arm (the low-frequency ripple component of the generated capacitance voltage), the high-frequency bridge arm circulating current and the high-frequency zero-sequence voltage can be used for restraining and offsetting the low-frequency component, so that the effect of restraining the low-frequency ripple of the capacitance voltage is achieved.
In order to determine the high-frequency bridge arm circulating current and the high-frequency zero-sequence voltage which can inhibit low-frequency pulsation, the properties of a zero-order component and a double-frequency component generated by multiplying two sine functions with the same frequency are firstly expressed as follows:
the second term in equation (15) can be expressed as:
in order to cancel the low frequency component shown in the first term in equation (15), it is necessary to satisfy:
according to the formulas (17) and (18), the formula (15) is simplified into:
according to equation (19), the pulsating power in the bridge arm can be modulated from the low frequency band to the high frequency band.
For high-frequency zero-sequence voltage and high-frequency bridge arm circulation, the following constraint conditions need to be met:
1) The same high-frequency zero-sequence voltage is respectively superposed on the three-phase output voltage instruction, and the high-frequency bridge arm circulating current of each phase is respectively superposed on the bridge arm circulating current instruction of the corresponding phase;
2) In order to reduce the current stress of the bridge arm, the high-frequency bridge arm circulating current is as small as possible, and the high-frequency zero-sequence voltage is as large as possible;
3) The high-frequency zero-sequence voltage should not cause the upper bridge arm and the lower bridge arm to generate overmodulation. At the fundamental output voltage u x Middle injection high frequency zero sequence voltage u cm The amplitude of the subsequent phase voltage should not exceed U dc 2, the high-frequency zero-sequence voltage is reduced along with the increase of the modulation ratio;
4) In consideration of factors such as dead zones, sampling errors and quantization errors, it is difficult to achieve a state of completely offsetting low-frequency pulsation, and in practical application, the high-frequency zero-sequence voltage should have a certain assignment margin.
In conclusion, the high-frequency zero-sequence voltage and the high-frequency bridge arm circulating current are determined and expressed as:
wherein, K cm The value range of the margin coefficient is 1.0-1.2; theta x An initial phase of the fundamental output voltage for the x-phase; considering that the capacity of the full-power frequency converter of the variable-speed pumping and storage unit is generally larger, the switching frequency of the system is not too high, and the high-frequency zero-sequence voltage and the high frequency areFrequency f of bridge arm circulation cm Can be taken out cm ＝6f n ，f n Rated working frequency of MMC frequency converter, angular frequency omega cm Can be dependent on the frequency f cm And (4) determining.
M is a modulation ratio, defined as the ratio of the amplitude of the phase output voltage to the half-bus dc voltage, which varies with the variation of the amplitude of the fundamental wave of the output voltage, and is expressed as:
referring to fig. 4, when the output frequency of the MMC frequency converter is lower than the first low frequency threshold, the high frequency zero sequence voltage u cm Enabling and injecting a three-phase output voltage u xref_o That is, the same high-frequency zero sequence voltage is respectively superposed on the three-phase output voltages a, b and c to obtain a first voltage modulation component u xref_1 Expressed as:
u xref_1 ＝u xref_o +u cm (23)
when the output frequency of the MMC frequency converter is lower than a second low-frequency threshold value, the high-frequency bridge arm current i of the x phase is converted into the high-frequency bridge arm current i of the x phase cmx Enabling and calculating high-frequency bridge arm current i cmx Bridge arm loop current i with x phase zx The difference is input into a double-proportion resonance controller, and a second voltage modulation wave component u is output by the controller xref_2 。
When the output frequency of the MMC frequency converter is between a second low-frequency threshold value and a first low-frequency threshold value, the high-frequency bridge arm current i of the x phase is converted into the high-frequency bridge arm current i of the x phase cmx Enabling, attenuating by an attenuation coefficient, and calculating the attenuated high-frequency bridge arm current i cmx Bridge arm loop current i with x phase zx The difference is input into a double-proportion resonance controller, and a second voltage modulation wave component u is output by the controller xref_2 。
After the first voltage modulation component and the second voltage modulation component are obtained, a driving signal for driving the frequency converter is generated according to the first voltage modulation component and the second voltage modulation component, so that the MMC frequency converter working according to the driving signal can effectively restrain low-frequency pulsation of capacitor voltage.
As shown in fig. 8, a simulation test of the capacitor voltage was performed according to the method provided in the present application. When the output frequency of the MMC frequency converter is 5Hz, high-frequency zero-sequence voltage is injected into three-phase output voltage, and high-frequency bridge arm circulating current is injected into bridge arm circulating current for restraining low-frequency pulsation of capacitance voltage; and when t =15s, the injection of the high-frequency zero-sequence voltage and the high-frequency bridge arm circulating current is stopped, and after 1s, the high-frequency zero-sequence voltage and the high-frequency bridge arm circulating current are injected again. According to test results, when the output frequency is lower than a certain threshold value, the low-frequency ripple of the capacitor voltage can be effectively inhibited by injecting the high-frequency zero-sequence voltage and the high-frequency bridge arm circulating current, after the injection is stopped, the ripple of the capacitor voltage is increased, the ripple amplitude is 13%, and after the injection is carried out again, the low-frequency ripple is rapidly converged, which shows that the high-frequency injection method provided by the application can effectively inhibit the low-frequency ripple of the capacitor voltage.
It should be noted that the method of the embodiment of the present application may be executed by a single device, such as a computer or a server. The method of the embodiment can also be applied to a distributed scene and completed by the mutual cooperation of a plurality of devices. In such a distributed scenario, one of the multiple devices may only perform one or more steps of the method of the embodiment, and the multiple devices interact with each other to complete the method.
It should be noted that the above description describes certain embodiments of the present disclosure. Other embodiments are within the scope of the following claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing may also be possible or may be advantageous.
As shown in fig. 9, an embodiment of the present application further provides a device for suppressing low-frequency ripple of a capacitor voltage of an MMC full-power frequency converter, including:
the modulation module is used for generating a first voltage modulation wave component according to a preset high-frequency zero-sequence voltage and a three-phase output voltage of the MMC frequency converter when the variable-speed pumped storage unit is in a variable-frequency starting or braking working condition and when the output frequency of the MMC frequency converter is in a preset range, and generating a second voltage modulation wave component according to a preset high-frequency bridge arm circulation current and a bridge arm circulation current of the MMC frequency converter; the high-frequency zero-sequence voltage is determined according to the phase output voltage amplitude, the bus direct-current voltage, a preset margin coefficient and the rated working frequency of the MMC frequency converter; the high-frequency bridge arm loop current is determined according to phase output current, the amplitude of the phase output voltage, bus direct-current voltage, the margin coefficient, the initial phase of fundamental wave voltage and the rated working frequency;
and the driving module is used for generating a driving signal according to the first voltage modulation wave component and the second voltage modulation wave component.
For convenience of description, the above devices are described as being divided into various modules by functions, and are described separately. Of course, the functions of the modules may be implemented in the same or multiple software and/or hardware when implementing the embodiments of the present application.
The apparatus of the foregoing embodiment is used to implement the corresponding method in the foregoing embodiment, and has the beneficial effects of the corresponding method embodiment, which are not described herein again.
Fig. 10 is a schematic diagram illustrating a more specific hardware structure of an electronic device according to this embodiment, where the electronic device may include: a processor 1010, a memory 1020, an input/output interface 1030, a communication interface 1040, and a bus 1050. Wherein the processor 1010, memory 1020, input/output interface 1030, and communication interface 1040 are communicatively coupled to each other within the device via bus 1050.
The processor 1010 may be implemented by a general-purpose CPU (Central Processing Unit), a microprocessor, an Application Specific Integrated Circuit (ASIC), or one or more Integrated circuits, and is configured to execute related programs to implement the technical solutions provided in the embodiments of the present disclosure.
The Memory 1020 may be implemented in the form of a ROM (Read Only Memory), a RAM (Random Access Memory), a static storage device, a dynamic storage device, or the like. The memory 1020 may store an operating system and other application programs, and when the technical solution provided by the embodiments of the present specification is implemented by software or firmware, the relevant program codes are stored in the memory 1020 and called to be executed by the processor 1010.
The input/output interface 1030 is used for connecting an input/output module to input and output information. The i/o module may be configured as a component within the device (not shown) or may be external to the device to provide corresponding functionality. Wherein the input devices may include a keyboard, mouse, touch screen, microphone, various sensors, etc., and the output devices may include a display, speaker, vibrator, indicator light, etc.
The communication interface 1040 is used for connecting a communication module (not shown in the drawings) to implement communication interaction between the present apparatus and other apparatuses. The communication module can realize communication in a wired mode (such as USB, network cable and the like) and also can realize communication in a wireless mode (such as mobile network, WIFI, bluetooth and the like).
It should be noted that although the above-mentioned device only shows the processor 1010, the memory 1020, the input/output interface 1030, the communication interface 1040 and the bus 1050, in a specific implementation, the device may also include other components necessary for normal operation. In addition, those skilled in the art will appreciate that the above-described apparatus may also include only those components necessary to implement the embodiments of the present description, and not necessarily all of the components shown in the figures.
The electronic device of the foregoing embodiment is used to implement the corresponding method in the foregoing embodiment, and has the beneficial effects of the corresponding method embodiment, which are not described herein again.
Computer-readable media, including both permanent and non-permanent, removable and non-removable media, for storing information may be implemented in any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static Random Access Memory (SRAM), dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), read Only Memory (ROM), electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information that can be accessed by a computing device.
Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, is limited to these examples; within the concept of the present disclosure, also technical features in the above embodiments or in different embodiments may be combined, steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present application described above, which are not provided in detail for the sake of brevity.
In addition, well-known power/ground connections to Integrated Circuit (IC) chips and other components may or may not be shown in the provided figures for simplicity of illustration and discussion, and so as not to obscure the embodiments of the application. Further, devices may be shown in block diagram form in order to avoid obscuring embodiments of the application, and this also takes into account the fact that specifics with respect to implementation of such block diagram devices are highly dependent upon the platform within which the embodiments of the application are to be implemented (i.e., specifics should be well within purview of one skilled in the art). Where specific details (e.g., circuits) are set forth in order to describe example embodiments of the disclosure, it should be apparent to one skilled in the art that the embodiments of the disclosure can be practiced without, or with variation of, these specific details. Accordingly, the description is to be regarded as illustrative instead of restrictive.
While the present disclosure has been described in conjunction with specific embodiments thereof, many alternatives, modifications, and variations of these embodiments will be apparent to those of ordinary skill in the art in light of the foregoing description. For example, other memory architectures, such as Dynamic RAM (DRAM), may use the discussed embodiments.
The present embodiments are intended to embrace all such alternatives, modifications and variances which fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalents, improvements, and the like that may be made without departing from the spirit or scope of the embodiments of the present disclosure are intended to be included within the scope of the disclosure.
Claims (10)
- The MMC full-power frequency converter capacitor voltage low-frequency ripple suppression method is characterized by comprising the following steps of:when the variable-speed pumped storage unit is in a variable-frequency starting or braking working condition, when the output frequency of the MMC frequency converter is in a preset range, generating a first voltage modulation wave component according to a preset high-frequency zero-sequence voltage and the three-phase output voltage of the MMC frequency converter, and generating a second voltage modulation wave component according to a preset high-frequency bridge arm circulation current and the bridge arm circulation current of the MMC frequency converter; the high-frequency zero-sequence voltage is determined according to the phase output voltage amplitude, the bus direct-current voltage, a preset margin coefficient and the rated working frequency of the MMC frequency converter; the high-frequency bridge arm loop current is determined according to phase output current, the amplitude of the phase output voltage, bus direct-current voltage, the margin coefficient, the initial phase of fundamental wave voltage and the rated working frequency;and generating a driving signal according to the first voltage modulation wave component and the second voltage modulation wave component.
- 2. The method of claim 1, wherein generating the first voltage modulation wave component according to the predetermined high frequency zero sequence voltage and the three-phase output voltage of the MMC frequency converter when the output frequency of the MMC frequency converter is in the predetermined range comprises:and when the output frequency is smaller than a preset first low-frequency threshold value, superposing the high-frequency zero-sequence voltage and the three-phase output voltage respectively to obtain the first voltage modulation wave component.
- 3. The method according to claim 2, wherein generating the second voltage-modulated wave component according to a predetermined high-frequency bridge-arm loop current and a bridge-arm loop current of the MMC frequency converter when the output frequency of the MMC frequency converter is in a predetermined range comprises:and when the output frequency is smaller than a preset second low-frequency threshold, regulating the high-frequency bridge arm circulating current by using a preset controller according to the bridge arm circulating current to obtain a second voltage modulation wave component.
- 4. The method according to claim 3, wherein the second voltage-modulated wave component is generated based on a predetermined high-frequency bridge-arm loop current and a bridge-arm loop current of the MMC frequency converter when the output frequency of the MMC frequency converter is in a predetermined range, further comprising:and when the output frequency is greater than the second low-frequency threshold and smaller than the first low-frequency threshold, attenuating the high-frequency bridge arm circulating current according to the output frequency, and adjusting the attenuated high-frequency bridge arm circulating current by using the controller according to the bridge arm circulating current to obtain the second voltage modulation wave component.
- 5. The method of claim 4, wherein attenuating the high frequency leg circulating current according to the output frequency comprises:determining an attenuation coefficient according to the output frequency;and attenuating the high-frequency bridge arm circulating current according to the attenuation coefficient.
- 6. The method of claim 3, wherein the controller is a dual proportional resonant controller; and after the high-frequency bridge arm circular current is adjusted by using a preset controller according to the bridge arm circular current, obtaining a second voltage modulation wave component, wherein the second voltage modulation wave component comprises the following steps:calculating the difference value between the high-frequency bridge arm circulation current and the bridge arm circulation current;and inputting the difference value into the double-proportion resonance controller, and outputting the second voltage modulation wave component by the double-proportion resonance controller.
- 7. The method according to any one of claims 1-6, wherein the high frequency zero sequence voltage is determined according to formula (20):
wherein M is the ratio of the amplitude of the phase output voltage to the half-bus DC voltage, U dc Is a DC bus voltage, K cm As a margin coefficient, ω cm Is an angular frequency determined from the nominal operating frequency. - 8. The method of claim 7, wherein the high frequency leg loop current is determined according to equation (21):
wherein, theta x Initial phase of the output voltage for x-phase, i x X = a, b, c, ω, for the output current of the x-phase out Is the AC output angular frequency of the MMC frequency converter. - 9. The method of claim 6, wherein the transfer function of the dual proportional resonant controller is:
wherein, K p Is a proportional gain factor, K r Is the resonant gain coefficient, omega i To account for the resonance term bandwidth of the-3 dB requirement, s is the Laplace operator, ω out The AC output angular frequency of the MMC frequency converter is obtained. - MMC full-power converter capacitor voltage low-frequency ripple suppression device, its characterized in that includes:the modulation module is used for generating a first voltage modulation wave component according to a preset high-frequency zero-sequence voltage and a three-phase output voltage of the MMC frequency converter when the variable-speed pumped storage unit is in a variable-frequency starting or braking working condition and when the output frequency of the MMC frequency converter is in a preset range, and generating a second voltage modulation wave component according to a preset high-frequency bridge arm circulation current and a bridge arm circulation current of the MMC frequency converter; the high-frequency zero-sequence voltage is determined according to the phase output voltage amplitude, the bus direct-current voltage, a preset margin coefficient and the rated working frequency of the MMC frequency converter; the high-frequency bridge arm circulating current is determined according to phase output current, the amplitude of the phase output voltage, bus direct-current voltage, the margin coefficient, the initial phase of fundamental voltage and the rated working frequency;and the driving module is used for generating a driving signal according to the first voltage modulation wave component and the second voltage modulation wave component.
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