CN117134429A - Power and harmonic output coordination control system and method based on variable switching frequency - Google Patents
Power and harmonic output coordination control system and method based on variable switching frequency Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention belongs to the technical field of power electronic converters, and particularly relates to a power and harmonic output coordination control system and method based on variable switching frequency, wherein the system comprises a power output part, a harmonic compensation part and a logic switching part; the power output part adopts a voltage outer ring and a current inner ring with low switching frequency for control, the harmonic compensation part adopts a multi-harmonic current control ring with high switching frequency, the switching part has independent output and mixed output modes according to the output power of the converter, and the converter can simultaneously perform power output and harmonic compensation in the mixed output mode, so that the characteristics of combining the electric energy management and the power output of the converter are realized, and the multifunctional effect of the converter is achieved.
Description
Technical Field
The invention belongs to the technical field of power electronic converters, and particularly relates to a power and harmonic output coordination control system and method based on variable switching frequency.
Background
The development of economy and society promotes the continuous increase of the demand of human beings for energy, and the development and wide use of new energy have become hot spots for the development of power grid energy. The converter used for generating the new energy is a full-power converter, so that the output current THD is less than 5%, and the design value of the filter inductor is larger. For the traditional grid-connected converter, only the active power with rated capacity can be output, and low-frequency harmonic waves generated by dead zone effect and the like cannot be subjected to harmonic compensation through self control, so that a corresponding harmonic compensation device is usually incorporated at an alternating current coupling point of the converter. And the addition of the harmonic compensation device increases the cost of the grid-connected converter system. Therefore, a grid-connected converter is needed to realize the functions of active reactive power output and harmonic compensation at the same time.
The invention patent with publication number of CN 112803457A discloses an energy storage system of a wind power converter and a control method thereof, wherein the DC conversion side of the energy storage system is connected with a DC bus of the wind power converter in parallel, the AC side of the energy storage system is connected with a grid-connected point of the wind power converter, double-contact fusion of the wind power converter and the energy storage system is realized, the fusion degree of the wind power converter and the energy storage system is remarkably improved, and the capacity of the energy storage system for participating in unit adjustment is improved; and the control unit can control the running state of the energy storage system, namely, the energy storage system is controlled to be in at least one of an alternating current side coupling state and a direct current side coupling state so as to realize the switching of different functions and control targets, and further, the wind power converter energy storage system has redundancy reliability.
The invention patent of publication number CN 101931241A discloses a grid-connected coordination control method for a wind farm, and belongs to the technical field of grid-connected control for the wind farm; the coordination control of the wind power plant is to collect information of a single machine device, analyze the collected information by the wind power plant and apply the information to power grid dispatching; according to the three-level combined coordination framework of the fan, the wind farm and the power grid, the functions and mutual coordination relation of all levels of links are completely realized, so that the whole wind farm presents the operation and regulation characteristics of the traditional power plant to the power grid, the impact and influence of the wind farm on the power grid are reduced, and even necessary support is provided for frequency modulation, voltage regulation and the like of the power grid; the invention stands in global and macroscopic angles, and utilizes the combination coordination and mutual support of the transverse whole and the longitudinal whole through the support of modern communication and analysis computing technology capability to eliminate or reduce the defects and negative effects of the individual fans, thereby ensuring that the whole wind farm presents friendly characteristics for a power grid, improving the number of grid-connected operation hours and greatly improving the economic benefit.
In the prior art, the grid-connected converter can realize power output through an optimized control strategy, and can output harmonic current of partial harmonic frequency; however, due to the limitation of the size of the output filter inductor, if the converter outputs harmonic current with larger harmonic frequency, the converter is inevitably required to inversely change large harmonic voltage, and other harmonic frequency is easily generated due to the overshoot of the modulator; decreasing the filter inductance increases the current ripple amplitude and increases the current THD. Therefore, a coordinated control method capable of simultaneously outputting active current and harmonic current under low filter inductance needs to be provided.
Disclosure of Invention
The invention aims to provide a power and harmonic wave output coordination control system and method based on variable switching frequency, aiming at the problems in the prior art.
The technical scheme of the invention is as follows:
the power and harmonic output coordination control system based on the variable switching frequency is suitable for controlling a converter adopted by new energy power generation and comprises a power output module, a harmonic compensation module, an inverse Peak conversion and logic switching module;
the three currents i and the three-phase voltages u of the collected converter are processed by a park transformation module and then are simultaneously input into a power output module and a harmonic compensation module; the output current d of the converter is obtained through the processing of the power output moduleAxis component reference value i d Reference value u of d-axis component of output voltage of current transformer d Reference value u of q-axis component of output voltage of current transformer q * The method comprises the steps of carrying out a first treatment on the surface of the The harmonic compensation module is used for processing to obtain a d-axis component reference value u of the k-th harmonic voltage output by the converter dk Output k harmonic voltage q-axis component reference value u of current transformer qk A (E); output current d-axis component reference value i of output converter d Reference value u of d-axis component of output voltage of current transformer d Reference value u of q-axis component of output voltage of sum current transformer q * Inputting the converted signals to a logic switching module after inverse Peak conversion; the control logic of the logic switching module is that the output power is larger than the minimum output power P min When the low-frequency module is switched to be independently output, a low-frequency PWM signal is output; the output power is smaller than the minimum output power P min And when the switching switch is switched to the mixed output high-frequency module to output the high-frequency PWM signal.
Specifically, the harmonic compensation module comprises a plurality of harmonic current controllers.
Specifically, the power output module comprises a direct voltage control module and a current control module, wherein the direct voltage control module is used for sampling the direct-current side voltage u of the converter dc And a DC voltage reference value u dcref The phase difference, the negative value of the difference value is input into a first proportional integral controller to obtain the d-axis component reference value i of the current output by the converter d A (E); the control mode of the current control is that the sampled converter output current is subjected to the output current d-axis component i obtained by a park conversion module d Q-axis component i q Respectively and d-axis component reference value i of current output by converter d Reference value i of q-axis component of output current of phase difference transformer q The difference of the positive and negative values is respectively input into a second proportional-integral controller and a third proportional-integral controller, and the output value is respectively matched with the d-axis component u of the output voltage d Adding and outputting the q-axis component u of the voltage q Adding to obtain the d-axis component reference value u of the output voltage of the converter d Sum q-axis component reference value u q *。
Specifically, the logic switching module comprises a switching module, an independent output low-frequency module and a mixed output high-frequency module.
Specifically, the control method using the power and harmonic output coordination control system based on the variable switching frequency comprises the following steps:
s1, collecting three currents i and three-phase voltages u of a current transformer;
s2, processing the three currents i and the three-phase voltages u of the acquired converter by a park transformation module and then inputting the three currents i and the three-phase voltages u to a power output module and a harmonic compensation module at the same time;
s3, obtaining a q-axis component reference value u of the output voltage of the converter through direct voltage control and current control of the power output module q * And the d-axis component reference value u of the output voltage of the converter d *；
S4, processing by a harmonic compensation module to obtain a q-axis component reference value u of the k-order harmonic voltage output by the converter qk * And the d-axis component reference value u of the k-th harmonic voltage output by the converter dk Where k is a singular number of at least 3;
s5, outputting a d-axis component reference value i of the output current of the converter dk Reference value u of d-axis component of output voltage of current transformer dk Reference value u of q-axis component of output voltage of sum current transformer qk * Inputting the converted signals to a logic switching module after inverse Peak conversion;
s6, the logic switching module sets the control logic to be that the output power is larger than the minimum output power P min When the switching switch is switched to the single output low-frequency module to output a low-frequency PWM signal; the output power is smaller than the minimum output power P min And when the switching switch is switched to the mixed output high-frequency module to output the high-frequency PWM signal.
Specifically, the voltage control and the current control in the step S3 include the following steps:
A. the voltage control is to sample the DC side voltage u of the converter dc And a DC voltage reference value u dcref Performing difference to obtain a difference value between the sampling voltage and the direct current reference voltage;
B. the difference value of the two voltages obtained in the steps is taken as a negative value and then is input into a first proportional-integral controller to obtain the output of the converterD-axis component reference value i of current d ＊；
C. The current control is to obtain an output current d-axis component i by passing the sampled converter output current through a park conversion module d With reference value i of d-axis component of output current of converter d Performing difference to obtain a difference value of the two;
D. inputting the negative value of the difference between the two currents obtained in the steps into a second proportional-integral controller, and outputting the output value of the proportional-integral controller and the d-axis component u of the output voltage d Adding to obtain the d-axis component reference value u of the output voltage of the converter d ＊；
E. Output current q-axis component i obtained by the converter output current i through park conversion module q Reference value i of q-axis component of output current of converter q The difference of the phase difference, the negative value of the difference is input into a third proportional-integral controller, and the output value and the q-axis component u of the output voltage q Adding to obtain a q-axis component reference value u of the output voltage of the converter q * 。
Specifically, the processing of the harmonic compensation module in the above steps includes the following steps:
a) The sampled converter output current passes through a park conversion module of k phases to obtain d-axis and q-axis components of the kth harmonic current;
b) The d-axis component and the q-axis component of the kth harmonic current are filtered to obtain the d-axis component and the i-axis component of the kth harmonic current dk And the difference value is obtained by the difference between the current transformer output harmonic voltage and 0, the negative value of the difference value is input into a 2n+2-th proportional-integral controller to control the difference value, and the d-axis component reference value u of the current transformer output harmonic voltage k times is obtained dk Where k is a singular number of at least 3 and n is a natural number other than 0;
c) The output current of the converter is subjected to a park transformation module under k phases and k harmonic currents obtained by filtering treatment to obtain an output current q-axis component i qk And a negative value of the difference value is input into a 2n+3-th proportional-integral controller to obtain a q-axis component reference value u of the output k-th harmonic voltage of the converter qk Where k is a singular number of at least 3 and n is a natural number other than 0.
Specifically, the processing of the logic switching module comprises the following steps:
a. setting the control logic of the switching module to output power greater than the minimum output power P min When the switching switch is switched to the single output low-frequency module; the output power is smaller than the minimum output power P min When the switch is switched to the mixed output high-frequency module
b. The single output low frequency module outputs the current transformer output voltage dq axis component reference value u of the power output part d *、u q * Converter output voltage u output by inverse Peak conversion module abc *；
c. Will inverse Peak transform output voltage u abc * Inputting a low-frequency SPWM modulator, and finally outputting a low-frequency PWM signal by the SPWM modulator;
d. the independent output high-frequency module is a power output part and a low-frequency modulator part, and the control logic is a reference value u of the dq axis component of the converter output voltage outputted by the power output part d *、u q * Converter output voltage u output by inverse Peak conversion module abc * ；
e. The converter outputs k times voltage dq axis component reference value u d * 、u q * The converter output k times of voltage u output by the inverse Peak conversion module abck * With voltage u output by power output part abc * And adding, wherein the added value is input into a high-frequency SPWM modulator, and a high-frequency PWM signal is output, wherein k is a singular number of which the minimum is 3, and n is a natural number which is not 0.
Specifically, the minimum output power P in the switching module min Is selected as shown in the following formula:
minimum output power P in the switching module min In the selection, the switching frequency of the low-frequency modulator is f s1 The switching frequency of the high-frequency modulator is f s2 Converter capacity at low switching frequency is S n The effective value of the phase voltage of the power grid is U s The impedance between the converter and the power grid is X.
The beneficial effects of the invention are as follows: the control system comprises a power output part, a harmonic compensation part and a logic switching part; the power output part adopts voltage control and current control with low switching frequency, the harmonic compensation part adopts a multi-harmonic current control loop with high switching frequency, and the switching part has independent output and mixed output modes according to the output power of the converter; the power output and the harmonic compensation of the converter can be simultaneously carried out in the mixed output mode, the characteristics of combining the electric energy management and the power output of the converter are realized, the multifunctional effect of the converter is achieved, the converter system with smaller filter parameters can be adapted, and the harmonic compensation is realized under certain transmission power.
Drawings
Fig. 1 is a block diagram of a control system according to the present invention.
Fig. 2 is a schematic diagram of a power output module according to the present invention;
fig. 3 is a schematic diagram of a harmonic output module according to the present invention;
fig. 4 is a schematic diagram of a logic switching module according to the present invention.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and the specific embodiments.
Example 1
As shown in fig. 1, the control system provided by the invention is a structural block diagram, and is applicable to control of a converter used for generating new energy based on a power and harmonic output coordination control system with variable switching frequency, and comprises a power output module, a harmonic compensation module, an inverse Peak conversion and logic switching module;
the three currents i and the three-phase voltages u of the collected converter are processed by a park transformation module and then are simultaneously input into a power output module and a harmonic compensation module; the d-axis component reference value i of the output current of the converter is obtained through the processing of the power output module d ＊ D-axis component reference value u of converter output voltage d ＊ Reference value u of q-axis component of output voltage of converter q * The method comprises the steps of carrying out a first treatment on the surface of the The harmonic compensation module is used for processing to obtain a d-axis component reference value u of the k-th harmonic voltage output by the converter dk ＊ Converter output k-th harmonic voltage q-axis component reference value u qk ＊ The method comprises the steps of carrying out a first treatment on the surface of the Output current d-axis component reference value i of output converter d ＊ D-axis component reference value u of converter output voltage d * And a q-axis component reference value u of the output voltage of the converter q * Inputting the converted signals to a logic switching module after inverse Peak conversion; the control logic of the logic switching module is that the output power is larger than the minimum output power P min When the low-frequency module is switched to be independently output, a low-frequency PWM signal is output; the output power is smaller than the minimum output power P min And when the switching switch is switched to the mixed output high-frequency module to output the high-frequency PWM signal.
The harmonic compensation module comprises a plurality of harmonic current controllers.
The power output module comprises a direct voltage control module and a current control module, wherein the direct voltage control module is used for sampling the direct-current side voltage u of the converter dc And a DC voltage reference value u dcref The phase difference, the negative value of the difference value is input into a first proportional integral controller to obtain the d-axis component reference value i of the current output by the converter d ＊ The method comprises the steps of carrying out a first treatment on the surface of the The control mode of the current control is that the sampled converter output current is subjected to the output current d-axis component i obtained by a park conversion module d Q-axis component i q Respectively and d-axis component reference value i of current output by converter d ＊ Phase difference, converter output current q-axis component reference value i q ＊ The negative value of the difference value is respectively input into a second proportional-integral controller and a third proportional-integral controller, and the output value is respectively matched with the d-axis component u of the output voltage d Adding and outputting the q-axis component u of the voltage q Adding to obtain the d-axis component reference value u of the output voltage of the converter d ＊ And q-axis component reference value u q * 。
The logic switching module comprises a switching module, a single output low-frequency module and a mixed output high-frequency module.
Example 2
The embodiment provides a control method of a power and harmonic output coordination control system based on variable switching frequency, which comprises the following steps:
s1, collecting three currents i and three-phase voltages u of a current transformer;
s2, processing the three currents i and the three-phase voltages u of the acquired converter by a park transformation module and then inputting the three currents i and the three-phase voltages u to a power output module and a harmonic compensation module at the same time;
s3, obtaining a q-axis component reference value u of the output voltage of the converter through direct voltage control and current control of the power output module q * And the d-axis component reference value u of the output voltage of the converter d *；
S4, processing by a harmonic compensation module to obtain a q-axis component reference value u of the k-order harmonic voltage output by the converter qk Reference value u of d-axis component of harmonic voltage of output k of converter dk Where k is a singular number of at least 3;
s5, outputting a d-axis component reference value i of the output current of the converter dk Reference value u of d-axis component of output voltage of current transformer dk Reference value u of q-axis component of output voltage of sum current transformer qk * Inputting the converted signals to a logic switching module after inverse Peak conversion;
s6, the logic switching module sets the control logic to be that the output power is larger than the minimum output power P min When the switching switch is switched to the single output low-frequency module to output a low-frequency PWM signal; the output power is smaller than the minimum output power P min And when the switching switch is switched to the mixed output high-frequency module to output the high-frequency PWM signal.
Example 3
The embodiment provides control of the power output module, as shown in fig. 2, which is a schematic diagram of the principle structure, and includes voltage control and current control, and includes the following steps:
A. the voltage control is to sample the DC side voltage u of the converter dc And a DC voltage reference value u dcref Taking the difference to obtain the sampling voltage and the direct current referenceA difference in voltage;
B. the difference value of the two voltages in the step is taken as a negative value and then is input into a first proportional integral controller to obtain a d-axis component reference value i of the output current of the converter d ＊；
C. The control of the current control is that the sampled converter output current is subjected to the output current d-axis component i obtained by a park conversion module d With reference value i of d-axis component of output current of converter d Performing difference to obtain a difference value of the two;
D. inputting the negative value of the difference between the two currents obtained in the steps into a second proportional-integral controller, and outputting the output value of the proportional-integral controller and the d-axis component u of the output voltage d Adding to obtain the d-axis component reference value u of the output voltage of the converter d ＊；
E. Output current q-axis component i obtained by the converter output current i through park conversion module q Reference value i of q-axis component of output current of converter q The difference of the phase difference, the negative value of the difference is input into a third proportional-integral controller, and the output value and the q-axis component u of the output voltage q Adding to obtain a q-axis component reference value u of the output voltage of the converter q * 。
Example 4
The schematic diagram of the control process of the harmonic compensation module is shown in fig. 3, and the harmonic compensation module includes a plurality of harmonic current controllers, including the following steps:
a) The sampled converter output current passes through a park conversion module of k phases to obtain d-axis and q-axis components of the kth harmonic current;
b) Inputting the dq-axis component of the kth harmonic current into a filter module to obtain the d-axis component i of the kth harmonic current dk And the difference value is obtained by the difference between the current transformer output harmonic voltage and 0, the negative value of the difference value is input into a 2n+2-th proportional-integral controller to control the difference value, and the d-axis component reference value u of the current transformer output harmonic voltage k times is obtained dk ＊；
C) The output current q-axis component i of the current transformer output current obtained by the k-order harmonic current obtained by the park transformation module and the filtering module under the k-order phase qk And a negative value of the difference value is input into a 2n+3-th proportional-integral controller to obtain a q-axis component reference value u of the output k-th harmonic voltage of the converter qk Where k= 3,5,7,11,13, … …, n=1, 2,3, … …;
example 5
The embodiment provides control processing of a logic switching module, wherein the logic switching module comprises a switching module, an independent output low-frequency module and a mixed output high-frequency module; the processing comprises the following steps:
a. setting the control logic of the switching module to output power greater than the minimum output power P min When the switching switch is switched to the single output low-frequency module; the output power is smaller than the minimum output power P min When the output power is calculated, the change-over switch is switched to the mixed output high-frequency module, and the output power calculation expression is as follows:
P＝u d i d +u q i q ；
b. the single output low frequency module outputs the current transformer output voltage dq axis component reference value u of the power output part d ＊、u q Output voltage u of converter output by inverse Peak conversion module abc ＊；
c. Will inverse Peak transform output voltage u abc Inputting the signal into a low-frequency SPWM modulator, and finally outputting a low-frequency PWM signal by the SPWM modulator;
d. the independent output high-frequency module is a power output part and a low-frequency modulator part, and the control logic is a reference value u of the dq axis component of the converter output voltage outputted by the power output part d ＊、u q Output voltage u of converter output by inverse Peak conversion module abc ＊；
e. The converter outputs k times voltage dq axis component reference value u d ＊、u q The current transformer output k times of voltage u output by the inverse Peak conversion module abck Voltage u output by the output section of the sum power abc The sum is input to a high frequency SPWM modulator, which outputs a high frequency PWM signal, where k= 3,5,7,11,13, … …, n=1, 2,3, … ….
Minimum of the switching modulesOutput power P min Is selected as shown in the following formula:
minimum output power P in the switching module min In the selection, the switching frequency of the low-frequency modulator is f s1 The switching frequency of the high-frequency modulator is f s2 Converter capacity at low switching frequency is S n The effective value of the phase voltage of the power grid is U s The impedance between the converter and the power grid is X. Finally, it should be noted that the above-mentioned embodiments are only for illustrating the technical scheme of the present invention and are not limiting; while the invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that: modifications may be made to the specific embodiments of the present invention or equivalents may be substituted for part of the technical features thereof; without departing from the spirit of the invention, it is intended to cover the scope of the invention as claimed.
Claims (9)
1. The power and harmonic output coordination control system based on the variable switching frequency is suitable for controlling a converter adopted by new energy power generation and is characterized by comprising a power output module, a harmonic compensation module, an inverse Paeke conversion and logic switching module;
the three currents i and the three-phase voltages u of the collected converter are processed by a park transformation module and then are simultaneously input into a power output module and a harmonic compensation module; the d-axis component reference value i of the output current of the converter is obtained through the processing of the power output module d ＊ D-axis component reference value u of converter output voltage d ＊ Reference value u of q-axis component of output voltage of converter q * The method comprises the steps of carrying out a first treatment on the surface of the The harmonic compensation module is used for processing to obtain a d-axis component reference value u of the k-th harmonic voltage output by the converter dk ＊ Converter output k-th harmonic voltage q-axis component reference value u qk ＊ The method comprises the steps of carrying out a first treatment on the surface of the Output current d-axis component reference value i of output converter d ＊ Current transformerOutput voltage d-axis component reference value u d ＊ And a q-axis component reference value u of the output voltage of the converter q * Inputting the converted signals to a logic switching module after inverse Peak conversion; the control logic of the logic switching module is that the output power is larger than the minimum output power P min When the low-frequency module is switched to be independently output, a low-frequency PWM signal is output; the output power is smaller than the minimum output power P min And when the switching switch is switched to the mixed output high-frequency module to output the high-frequency PWM signal.
2. The variable switching frequency based power and harmonic output coordination control system of claim 1 wherein the harmonic compensation module comprises a plurality of harmonic current controllers.
3. The power and harmonic output coordinated control system based on variable switching frequency according to claim 1, wherein the power output module comprises a direct voltage control module and a current control module, the direct voltage control module is used for sampling the direct current side voltage u of the converter dc And a DC voltage reference value u dcref The phase difference, the negative value of the difference value is input into a first proportional integral controller to obtain the d-axis component reference value i of the current output by the converter d ＊ The method comprises the steps of carrying out a first treatment on the surface of the The control mode of the current control is that the sampled converter output current is subjected to the output current d-axis component i obtained by a park conversion module d Q-axis component i q Respectively and d-axis component reference value i of current output by converter d ＊ Phase difference, converter output current q-axis component reference value i q ＊ The negative value of the difference value is respectively input into a second proportional-integral controller and a third proportional-integral controller, and the output value is respectively matched with the d-axis component u of the output voltage d Adding and outputting the q-axis component u of the voltage q Adding to obtain the d-axis component reference value u of the output voltage of the converter d ＊ And q-axis component reference value u q * 。
4. The variable switching frequency based power and harmonic output coordination control system of claim 1, wherein the logic switching module comprises a switching module, a separate output low frequency module, and a mixed output high frequency module.
5. A control method using the variable switching frequency-based power and harmonic output coordination control system according to any one of claims 1 to 4, comprising the steps of:
s1, collecting three currents i and three-phase voltages u of a current transformer;
s2, processing the three currents i and the three-phase voltages u of the acquired converter by a park transformation module and then inputting the three currents i and the three-phase voltages u to a power output module and a harmonic compensation module at the same time;
s3, obtaining a q-axis component reference value u of the output voltage of the converter through direct voltage control and current control of the power output module q * And the d-axis component reference value u of the output voltage of the converter d * ；
S4, processing by a harmonic compensation module to obtain a q-axis component reference value u of the k-order harmonic voltage output by the converter qk ＊ And the d-axis component reference value u of the k-th harmonic voltage output by the converter dk ＊ Where k is the singular number of at least 3;
s5, outputting a d-axis component reference value i of the output current of the converter dk ＊ D-axis component reference value u of converter output voltage dk ＊ And a q-axis component reference value u of the output voltage of the converter qk * Inputting the converted signals to a logic switching module after inverse Peak conversion;
s6, the logic switching module sets the control logic to be that the output power is larger than the minimum output power P min When the switching switch is switched to the single output low-frequency module to output a low-frequency PWM signal; the output power is smaller than the minimum output power P min And when the switching switch is switched to the mixed output high-frequency module to output the high-frequency PWM signal.
6. The control method of the power and harmonic output coordination control system based on variable switching frequency according to claim 5, wherein the voltage control and the current control in step S3 comprise the following steps:
A. the voltage control is to sample the DC side voltage u of the converter dc And a DC voltage reference value u dcref Performing difference to obtain a difference value between the sampling voltage and the direct current reference voltage;
B. the difference value of the two voltages obtained in the steps is taken as a negative value and then is input into a first proportional integral controller to obtain a d-axis component reference value i of the output current of the converter d ＊；
C. The current control is to obtain an output current d-axis component i by passing the sampled converter output current through a park conversion module d With reference value i of d-axis component of output current of converter d Performing difference to obtain a difference value of the two;
D. inputting the negative value of the difference between the two currents obtained in the steps into a second proportional-integral controller, and outputting the output value of the proportional-integral controller and the d-axis component u of the output voltage d Adding to obtain the d-axis component reference value u of the output voltage of the converter d ＊；
E. Output current q-axis component i obtained by the converter output current i through park conversion module q Reference value i of q-axis component of output current of converter q The difference of the phase difference, the negative value of the difference is input into a third proportional-integral controller, and the output value and the q-axis component u of the output voltage q Adding to obtain a q-axis component reference value u of the output voltage of the converter q * 。
7. The control method of the power and harmonic output coordination control system based on variable switching frequency according to claim 5, wherein the processing of the harmonic compensation module comprises the steps of:
a) The sampled converter output current passes through a park conversion module of k phases to obtain d-axis and q-axis components of the kth harmonic current;
b) The d-axis component and the q-axis component of the kth harmonic current are filtered to obtain the d-axis component and the i-axis component of the kth harmonic current dk And the difference value is obtained by the difference between the input voltage and the output voltage, and the difference value is controlled by a 2n+2-th proportional-integral controller to obtain the output voltage of the converterYielding a reference value u for the d-axis component of the k-th harmonic voltage dk * Where k is a singular number of at least 3 and n is a natural number other than 0;
c) The output current of the converter is subjected to a park transformation module under k phases and k harmonic currents obtained by filtering treatment to obtain an output current q-axis component i qk And a negative value of the difference value is input into a 2n+3-th proportional-integral controller to obtain a q-axis component reference value u of the output k-th harmonic voltage of the converter qk * Where k is a singular number of at least 3 and n is a natural number other than 0.
8. The control method of the power and harmonic output coordination control system based on variable switching frequency according to claim 5, wherein the processing of the logic switching module comprises the following steps:
a. setting the control logic of the switching module to output power greater than the minimum output power P min When the switching switch is switched to the single output low-frequency module; the output power is smaller than the minimum output power P min When the switch is switched to the mixed output high-frequency module
b. The single output low frequency module outputs the current transformer output voltage dq axis component reference value u of the power output part d *、u q * Converter output voltage u output by inverse Peak conversion module abc *；
c. Will inverse Peak transform output voltage u abc * Inputting a low-frequency SPWM modulator, and finally outputting a low-frequency PWM signal by the SPWM modulator;
d. the independent output high-frequency module is a power output part and a low-frequency modulator part, and the control logic is a reference value u of the dq axis component of the converter output voltage outputted by the power output part d *、u q * Converter output voltage u output by inverse Peak conversion module abc *；
e. The converter outputs k times voltage dq axis component reference value u d *、u q * The converter output k times of voltage u output by the inverse Peak conversion module abck * With voltage u output by power output part abc * Adding, the added value is input into a high-frequency SPWM modulator, and outputA high frequency PWM signal, where k is a singular number of at least 3 and n is a natural number other than 0.
9. The control method of a power and harmonic output coordination control system based on a variable switching frequency according to claim 5 or 8, wherein the minimum output power P in the switching module min Is selected as shown in the following formula:
minimum output power P in the switching module min In the selection, the switching frequency of the low-frequency modulator is f s1 The switching frequency of the high-frequency modulator is f s2 Converter capacity at low switching frequency is S n The effective value of the phase voltage of the power grid is U s The impedance between the converter and the power grid is X.
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