Power transmission harmonic suppression method, system and equipment based on direct current, and medium

Abstract

The invention provides a power transmission harmonic suppression method, system and device based on direct current and a medium. According to the method, the voltage source converter is controlled through a negative-sequence three-phase internal unbalanced voltage drop reference value, a modulation wave controlled and issued by the voltage source converter and an actual modulation wave, determined by a harmonic voltage component, of the voltage source converter, and the voltage source converter can be controlled on the premise that additional electrical equipment and control interfaces are not added. Other sub-harmonic components introduced into the hybrid cascade direct-current power transmission system are suppressed in a reasonable range, the harmonic components in the direct-current power transmission system are effectively suppressed, the use of additional filtering equipment is reduced, Park transformation and voltage feed-forward compensation links do not need to be carried out, and the implementation is relatively simple in engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current power transmission, and in particular to a method, system, equipment and medium for suppressing power transmission harmonics based on direct current. Background Art

[0002] Compared with AC transmission, DC transmission has the advantages of low line cost, large transmission capacity, interconnection between power grids of different frequencies, and no synchronization stability problems. It has developed rapidly in recent decades. At present, there are two main types of HVDC transmission technologies used in actual projects: line commuted converter based high voltage direct current (LCC-HVDC) and voltage source converter based high voltage direct current (VSC-HVDC) based on fully controlled devices.

[0003] LCC-HVDC has many advantages, such as simple structure, low cost, mature technology, high reliability, and suitability for long-distance and large-capacity power transmission. However, the grid-commutated converter (LCC) needs to absorb a large amount of reactive power when working, and both the AC and DC sides contain a large amount of harmonics, which requires additional reactive power compensation and AC and DC filtering devices, increasing the construction cost. At the same time, LCC-HVDC is limited by its own technology and has the problem of commutation failure. In contrast, VSC-HVDC uses fully controlled power electronic devices IGBT, which can independently adjust active power and reactive power, has low harmonic levels, and does not have the problem of commutation failure, but the cost is high.

[0004] In general, LCC-HVDC and VSC-HVDC each have their own advantages and disadvantages. In order to give full play to the advantages of the two types of DC transmission, these two different types of converters are used in the same DC transmission system. There are many different topological structures of hybrid DC transmission systems, such as LCC on the rectifier side and VSC on the inverter side, LCC on the rectifier side and LCC and VSC on the inverter side. Take the receiving end hybrid DC transmission system as an example, that is, LCC is used on the rectifier side, and the inverter side adopts a structure in which the high-pressure valve group LCC and the low-pressure valve group VSC are connected in parallel in series. This structure reduces the probability of commutation failure on the inverter side to a certain extent, and reduces the investment in reactive compensation devices and filtering links. Compared with the VSC structure, the hybrid structure has a larger transmission capacity, lower manufacturing difficulty, and lower cost.

[0005] However, the harmonic characteristics of this hybrid DC transmission system topology have a relatively large impact on the control and protection of the receiving-end hybrid LCC-VSC system, and the harmonic characteristics are more complex. If not suppressed, when the system parameters and controller parameters of the LCC and VSC are coupled, the risk of system oscillation increases significantly, which not only increases the electrical stress of the switching devices and primary equipment, but also may cause corresponding protection actions, and eventually cause the entire system to shut down. At present, the hybrid DC transmission system relies on adding additional filtering equipment to filter out the corresponding harmonics, which not only increases the equipment cost, but also has limited suppression effect. Summary of the invention

[0006] In order to solve the technical defects in the prior art, the present invention provides a method, system, device and medium for suppressing power transmission harmonics based on direct current.

[0007] A first aspect of the present invention provides a method for suppressing power transmission harmonics based on direct current, the method comprising:

[0008] Obtaining a DC current of a voltage source converter in a hybrid cascade DC power transmission system, an internal unbalanced voltage drop reference value of a negative sequence three-phase, and a modulation wave controlled and sent by the voltage source converter, wherein the negative sequence three-phase is a negative sequence component of a circulating current in the voltage source converter in the hybrid cascade DC power transmission system;

[0009] Using a low-pass filter and a first proportional resonant controller to perform commutation suppression control processing on the DC current of the voltage source converter to obtain a harmonic voltage component of the voltage source converter;

[0010] Based on the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave sent by the voltage source converter control and the harmonic voltage component, the actual modulation wave of the voltage source converter is calculated;

[0011] The voltage source converter is controlled based on the actual modulation wave of the voltage source converter.

[0012] Optionally, the using a low-pass filter and a first proportional resonant controller to perform commutation suppression control processing on the DC current of the voltage source converter to obtain the harmonic voltage component of the voltage source converter includes:

[0013] Based on the direct current of the voltage source converter, outputting the fluctuation amount of the direct current by using a low-pass filter;

[0014] The fluctuation amount of the DC current is input into a first proportional resonant controller, and the first transfer function in the first proportional resonant controller is used to output the harmonic voltage component of the voltage source converter, wherein the first transfer function is determined based on the proportional link gain, the resonant gain and bandwidth of the sixth resonant controller, and the resonant gain and bandwidth of the twelfth resonant controller.

[0015] Optionally, the first transfer function includes the following calculation formula:

[0016]

[0017] Among them, K p1 is the proportional link gain, K i6 is the resonant gain of the sixth resonant controller, K i12 is the resonant gain of the twelve-order resonant controller, ω c6 is the bandwidth of the sixth resonant controller, ω c12 is the bandwidth of the twelve-order resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, G PR1 (s) is the first transfer function, ΔU dump is the harmonic voltage component of the voltage source converter.

[0018] Optionally, the internal unbalanced voltage drop reference value of the negative-sequence three-phase is obtained as follows:

[0019] Obtaining a three-phase bridge arm current of the voltage source converter;

[0020] Taking the average value of the upper bridge arm current and the lower bridge arm current in the three-phase bridge arm current of the voltage source converter as the three-phase circulating current of the voltage source converter;

[0021] The difference between the three-phase circulating current and the circulating current reference value is input into a second proportional resonant controller, and the internal unbalanced voltage drop reference value of the negative-sequence three-phase is outputted using a second transfer function in the second proportional resonant controller, wherein the second transfer function is determined based on the proportional link gain of the doubled frequency circulating current, the resonant gain of the secondary resonant controller and the bandwidth of the secondary resonant controller.

[0022] Optionally, the second transfer function includes the following calculation formula:

[0023]

[0024] Among them, K p2 is the proportional gain of the double frequency circulating current, K i2 is the resonant gain of the secondary resonant controller, ω c2 is the bandwidth of the secondary resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, GPR2 (s) is the second transfer function, u cirj_ref It is the reference value of internal unbalanced voltage drop of negative sequence three phases.

[0025] Optionally, the actual modulation wave of the voltage source converter is calculated based on the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave sent by the voltage source converter control and the harmonic voltage component, including:

[0026] Calculating a first difference between an internal unbalanced voltage drop reference value of the negative-sequence three-phase and a modulation wave controlled by the voltage source converter;

[0027] Subtracting the first difference from the harmonic voltage component to obtain a second difference;

[0028] The second difference is used as the actual modulation wave of the voltage source converter.

[0029] Optionally, the controlling the voltage source converter based on the actual modulation wave of the voltage source converter comprises:

[0030] By outputting the actual modulation wave to the voltage source converter, the output current of the voltage source converter is controlled.

[0031] Based on the same inventive concept, the second aspect of the present invention provides a power transmission harmonic suppression system based on direct current, the system comprising:

[0032] A parameter acquisition unit, used for acquiring a DC current of a voltage source converter in a hybrid cascade DC power transmission system, an internal unbalanced voltage drop reference value of a negative sequence three-phase, and a modulation wave controlled and issued by the voltage source converter, wherein the negative sequence three-phase is a negative sequence component of a circulating current in the voltage source converter in the hybrid cascade DC power transmission system;

[0033] a harmonic voltage component determination unit, configured to perform commutation suppression control processing on the DC current of the voltage source converter by using a low-pass filter and a first proportional resonant controller to obtain a harmonic voltage component of the voltage source converter;

[0034] An actual modulation wave determination unit, configured to calculate an actual modulation wave of the voltage source converter based on an internal unbalanced voltage drop reference value of the negative sequence three-phase, a modulation wave controlled by the voltage source converter, and the harmonic voltage component;

[0035] A control unit is used to control the voltage source converter based on an actual modulation wave of the voltage source converter.

[0036] Optionally, the harmonic voltage component determination unit is specifically used to:

[0037] Based on the direct current of the voltage source converter, outputting the fluctuation amount of the direct current by using a low-pass filter;

[0038] The fluctuation amount of the DC current is input into a first proportional resonant controller, and the first transfer function in the first proportional resonant controller is used to output the harmonic voltage component of the voltage source converter, wherein the first transfer function is determined based on the proportional link gain, the resonant gain and bandwidth of the sixth resonant controller, and the resonant gain and bandwidth of the twelfth resonant controller.

[0039] Optionally, the first transfer function includes the following calculation formula:

[0040]

[0041] Among them, K p1 is the proportional link gain, K i6 is the resonant gain of the sixth resonant controller, K i12 is the resonant gain of the twelve-order resonant controller, ω c6 is the bandwidth of the sixth resonant controller, ω c12 is the bandwidth of the twelve-order resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, G PR1 (s) is the first transfer function, ΔU dump is the harmonic voltage component of the voltage source converter.

[0042] Optionally, the system further comprises: an unbalanced voltage drop reference value obtaining unit; the unbalanced voltage drop reference value obtaining unit is used to:

[0043] Obtaining a three-phase bridge arm current of the voltage source converter;

[0044] Taking the average value of the upper bridge arm current and the lower bridge arm current in the three-phase bridge arm current of the voltage source converter as the three-phase circulating current of the voltage source converter;

[0045] The difference between the three-phase circulating current and the circulating current reference value is input into a second proportional resonant controller, and the internal unbalanced voltage drop reference value of the negative-sequence three-phase is outputted using a second transfer function in the second proportional resonant controller, wherein the second transfer function is determined based on the proportional link gain of the doubled frequency circulating current, the resonant gain of the secondary resonant controller and the bandwidth of the secondary resonant controller.

[0046] Optionally, the second transfer function includes the following calculation formula:

[0047]

[0048] Among them, K p2 is the proportional gain of the double frequency circulating current, Ki2 is the resonant gain of the secondary resonant controller, ω c2 is the bandwidth of the secondary resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, G PR2 (s) is the second transfer function, u cirj_ref It is the reference value of internal unbalanced voltage drop of negative sequence three phases.

[0049] Optionally, the actual modulation wave determination unit is specifically configured to:

[0050] Calculating a first difference between an internal unbalanced voltage drop reference value of the negative-sequence three-phase and a modulation wave controlled by the voltage source converter;

[0051] Subtracting the first difference from the harmonic voltage component to obtain a second difference;

[0052] The second difference is used as the actual modulation wave of the voltage source converter.

[0053] Optionally, the control unit is specifically used to:

[0054] By outputting the actual modulation wave to the voltage source converter, the output current of the voltage source converter is controlled.

[0055] Based on the same inventive concept, a third aspect of the present invention provides a computer device, including: one or more processors;

[0056] The processor is used to store one or more programs;

[0057] When the one or more programs are executed by the one or more processors, the method for suppressing power transmission harmonics based on direct current as described in any one of the first aspects is implemented.

[0058] Based on the same inventive concept, the fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed, the method for suppressing power transmission harmonics based on direct current as described in any one of the first aspects is implemented.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The present invention provides a transmission harmonic suppression method, system, equipment and medium based on direct current. The method controls the voltage source converter by using the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave sent by the voltage source converter control and the actual modulation wave of the voltage source converter determined by the harmonic voltage component, and can suppress other subharmonic components introduced in the hybrid cascade direct current transmission system within a reasonable range without adding additional electrical equipment and control interface, and ensure that when the active power is not less than 10% of the rated power, the total harmonic current content of the bridge arm is suppressed to less than 1% of the fundamental frequency AC component during normal operation, and at all power operation points, the total harmonic content of the AC bus of the converter station is not greater than 1% of the fundamental component, the single odd harmonic content is not greater than 0.7% of the fundamental component, and the single even harmonic content is not greater than 0.3% of the fundamental component, effectively suppressing the harmonic components in the direct current transmission system, reducing the use of additional filtering equipment, and not requiring Parker transformation and voltage feedforward compensation links, and relatively simple engineering implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 A flow chart of a method for suppressing power transmission harmonics based on direct current provided by the present invention;

[0062] Figure 2 A flow chart of another method for suppressing power transmission harmonics based on direct current provided by the present invention;

[0063] Figure 3 A schematic diagram of a harmonic suppression control strategy based on direct current provided by the present invention;

[0064] Figure 4 A flow chart of another method for suppressing power transmission harmonics based on direct current provided by the present invention;

[0065] Figure 5 A schematic diagram of a double frequency circulating current suppression strategy provided by the present invention;

[0066] Figure 6 A block diagram of a DC current-based power transmission harmonic suppression system provided by the present invention;

[0067] Figure 7 A block diagram of a computer device provided by the present invention. DETAILED DESCRIPTION

[0068] The specific implementation mode of the present invention is described in detail, taking the result of adopting hybrid cascade DC technology at the receiving end, LCC at the high end, and VSC topology at the low end as an example, the problems existing in the existing hybrid cascade DC technology are described. For an LCC converter with a pulsation number of p, n=kp harmonics will be mainly generated on its DC side, where k is an arbitrary positive integer. In addition to considering the harmonics generated by itself, the VSC needs to additionally consider the harmonic currents injected by the equipment connected to the VSC, especially the harmonic currents injected by the LCC converter. According to the analysis of the VSC harmonic current spectrum, in addition to the 2nd harmonic, the 6th and 12th harmonic components account for a large proportion, which will cause additional losses in the converter valve and cause unstable control of the converter.

[0069] However, current technologies rarely conduct research on the harmonic characteristics of cascaded systems, and most rely on adding additional filtering equipment to filter out the corresponding harmonics, which not only increases equipment costs but also has limited suppression effects.

[0070] The scheme of the present invention is specifically described by the following examples.

[0071] Embodiment 1:

[0072] Figure 1 A flow chart of a method for suppressing power transmission harmonics based on direct current provided by the present invention, such as Figure 1 As shown, the DC current-based power transmission harmonic suppression method may include the following steps:

[0073] In step 101, a DC current of a voltage source converter in a hybrid cascade DC power transmission system, an internal unbalanced voltage drop reference value of a negative sequence three-phase, and a modulation wave sent by the voltage source converter control are obtained.

[0074] Among them, the negative-sequence three-phase is the negative-sequence component of the circulating current in the voltage source converter in the hybrid cascaded DC transmission system, and the modulation wave controlled and sent by the voltage source converter can be obtained by generating a modulation wave algorithm of the voltage source converter (for example: pulse width modulation, sinusoidal pulse width modulation or space vector modulation).

[0075] It should be noted that the DC current of the voltage source converter can be obtained by collecting DC current through a current sensor (for example, a Hall effect sensor, a resistive sensor, i.e., a shunt, a transformer or an optical fiber sensor, etc.) set on the voltage source converter in the hybrid cascade DC transmission system; the three-phase voltage data of the voltage source converter can be collected through a voltage sensor, and the internal unbalanced voltage drop reference value of the negative-sequence three-phase can be calculated using the positive-sequence, negative-sequence and zero-sequence solutions (for example, Park transform, Clark transform, etc.).

[0076] In step 102, a commutation suppression control process is performed on the DC current of the voltage source converter using a low-pass filter and a first proportional resonant controller to obtain a harmonic voltage component of the voltage source converter.

[0077] The low-pass filter may be an active low-pass filter, a passive low-pass filter or a digital low-pass filter, etc. The harmonic voltage component of the voltage source converter refers to the non-fundamental frequency component (i.e., the voltage component at the integer multiple frequency of the fundamental wave) existing in the output voltage of the converter, for example: the harmonic voltage component of the 2nd fundamental frequency, the harmonic voltage component of the 6th fundamental frequency or the harmonic voltage component of the 12th fundamental frequency.

[0078] In step 103, the actual modulation wave of the voltage source converter is calculated based on the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave sent by the voltage source converter control and the harmonic voltage component.

[0079] In this step, the specific implementation method can be: calculate the first difference between the internal unbalanced voltage drop reference value of the negative-sequence three-phase and the modulation wave controlled by the voltage source converter; calculate the difference between the first difference and the harmonic voltage component to obtain the second difference; and use the second difference as the actual modulation wave of the voltage source converter.

[0080] In step 104, the voltage source converter is controlled based on the actual modulation wave of the voltage source converter.

[0081] In this step, a possible implementation method may be: controlling the output current of the voltage source converter by outputting the actual modulation wave to the voltage source converter.

[0082] In view of the harmonic problem caused by the LCC-VSC hybrid cascade topology, the control strategy of detecting DC current is used to suppress harmonic current without adding additional primary equipment. That is, the present invention mainly solves the harmonic current problem of VSC (Voltage Source Converter) in the LCC-VSC (Line Commutated Converter-Voltage Source Converter) hybrid cascade DC system. In addition to the harmonics generated by itself, VSC needs to consider the harmonic current injected by LCC (Line Commutated Converter) to avoid the additional loss generated by the converter valve and the control instability of the converter.

[0083] The present invention provides a harmonic suppression strategy based on direct current that suppresses other subharmonic components introduced by the cascade system within a reasonable range without adding additional electrical equipment and control interfaces. By adding a harmonic suppression strategy, other subharmonic components introduced by the cascade system can be suppressed within a reasonable range without adding additional electrical equipment and control interfaces, and Parker transformation and voltage feedforward compensation links are not required, so the engineering implementation is relatively simple.

[0084] The above technical scheme can control the voltage source converter through the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave issued by the voltage source converter control and the actual modulation wave of the voltage source converter determined by the harmonic voltage component. Without adding additional electrical equipment and control interface, other subharmonic components introduced in the hybrid cascade DC transmission system can be suppressed within a reasonable range, ensuring that when the active power is not less than 10% of the rated power, the total harmonic current content of the bridge arm is suppressed to less than 1% of the fundamental frequency AC component during normal operation. Under all power operating points, the total harmonic content of the AC bus of the converter station is not greater than 1% of the fundamental component, the single odd-order harmonic content is not greater than 0.7% of the fundamental component, and the single even-order harmonic content is not greater than 0.3% of the fundamental component. The harmonic components in the DC transmission system are effectively suppressed, the use of additional filtering equipment is reduced, and there is no need to perform Park transformation and voltage feedforward compensation links. The engineering implementation is relatively simple.

[0085] Figure 2 A flow chart of another method for suppressing power transmission harmonics based on direct current provided by the present invention, such as Figure 2 As shown above Figure 1 The specific implementation of step 102 may include the following steps:

[0086] In step 1021, based on the direct current of the voltage source converter, a fluctuation amount of the direct current is outputted using a low-pass filter.

[0087] This step may be implemented as follows: inputting the DC current of the voltage source converter into a low-pass filter to obtain a filtered DC current, calculating the difference between the input DC current and the filtered DC current to obtain the fluctuation of the DC current.

[0088] In step 1022, the fluctuation amount of the direct current is input into a first proportional resonant controller, and a first transfer function in the first proportional resonant controller is used to output the harmonic voltage component of the voltage source converter.

[0089] The first transfer function is determined based on the proportional link gain, the resonant gain and bandwidth of the sixth-order resonant controller, and the resonant gain and bandwidth of the twelfth-order resonant controller.

[0090] A possible implementation of this step may be: inputting the fluctuation of the DC current as a complex variable into the transfer function in the first proportional resonant controller, and obtaining the harmonic voltage component of the voltage source converter through the transfer function calculation.

[0091] It should be noted that the first transfer function includes the following calculation formula:

[0092]

[0093] Among them, K p1 is the proportional link gain, K i6 is the resonant gain of the sixth resonant controller, K i12 is the resonant gain of the twelve-order resonant controller, ω c6 is the bandwidth of the sixth resonant controller, ω c12 is the bandwidth of the twelve-order resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, G PR1 (s) is the first transfer function, ΔU dump is the harmonic voltage component of the voltage source converter. The bandwidth of the sixth resonant controller ω c6 and the bandwidth of the 12th order resonant controller ω c12 Generally, 5rad / s to 15rad / s is used to reduce the sensitivity of the PR (Proportional Resonant Controller) controller to frequency. At the same time, in order to reduce the impact on the system, the parameters of the PR controller are set according to the ramp during the commissioning process. The fluctuation of the DC current can be taken as a complex variable s and input into G PR1 The calculation formula of (s) is used to calculate the harmonic voltage component ΔU of the voltage source converter. dump .

[0094] Since the bridge arm is mainly composed of the second, sixth and twelfth harmonics and the high-order harmonic content is very small, in order to simplify the controller design, it is only necessary to suppress the second, sixth and twelfth harmonics. This strategy can suppress the second harmonic and other 6n harmonics (mainly the 6th and 12th harmonics).

[0095] In order to reduce the harm caused by the 6th and 12th harmonics, the present invention designs a harmonic suppression strategy based on DC current. At the same time, in order to achieve zero-static tracking of the AC components of each bridge arm, a proportional resonance (PR) controller is adopted. Considering that the PR controller can suppress a certain frequency of different sequence components, there is no need for Park transformation and voltage feedforward compensation, so the engineering implementation is relatively simple.

[0096] For example, Figure 3 As shown, Figure 3A schematic diagram of a harmonic suppression control strategy based on direct current provided by the present invention, wherein the direct current I dc After passing through the low-pass filter, the fluctuation of DC current is obtained, and then passed through the PR controller G PR1 (s), the harmonic voltage component ΔU can be calculated by the first transfer function dump , and the modulation wave u sent by the converter control pwm_pcp And the input bridge arm current I is processed by the double frequency circulating current suppression controller arm The obtained voltage drop (i.e. the internal unbalanced voltage drop reference value u of the negative sequence three-phase cirj_ref ) to obtain the actual modulation wave u of the converter bridge arm pwm (i.e. the actual modulation wave of the voltage source converter). In the hybrid cascaded DC transmission system, in addition to the harmonics generated by the VSC itself, the harmonic current injected by the LCC must also be considered. The harmonic suppression strategy based on DC current can eliminate specific harmonics and reduce additional filtering equipment; the harmonic suppression strategy based on DC current obtains the harmonic components of the DC current through closed-loop control of the DC current, and achieves the harmonic suppression effect through a low-pass filter and a PR controller.

[0097] Figure 4 A flow chart of another method for suppressing power transmission harmonics based on direct current provided by the present invention is as follows: Figure 4 As shown above Figure 1 The internal unbalanced voltage drop reference value of the negative sequence three-phase in step 101 can be obtained as follows:

[0098] In S1, the three-phase bridge arm currents of the voltage source converter are obtained.

[0099] The three-phase bridge arm current of the voltage source converter refers to the current flowing from each phase bridge arm to the load (such as a motor, a power grid, etc.).

[0100] It should be noted that the three-phase bridge arm current of the voltage source converter can be obtained by collecting current through a current sensor provided on the voltage source converter; the three-phase bridge arm current of the voltage source converter can also be obtained by estimating using a mathematical model.

[0101] In S2, the average value of the upper bridge arm current and the lower bridge arm current in the three-phase bridge arm current of the voltage source converter is used as the three-phase circulating current of the voltage source converter.

[0102] For example, the three-phase bridge arm current may include the a-phase bridge arm current i a 、B-phase bridge arm current i b and the c-phase bridge arm current i c , calculate the upper arm current i in phase a bridge arm respectively ap and the lower bridge arm current i anThe average value of av , the upper arm current i in the b phase bridge arm bp and the lower bridge arm current i bn The average value of bv and the upper arm current i in the c phase bridge arm cp and the lower bridge arm current i cn The average value of cv , the average value i av , average value i bv and the average value i cv The a-phase circulating current i of the voltage source converter is cira 、b phase circulation i cirb and c-phase circulation i circ , we can get the three-phase circulating current i of the voltage source converter cirj .

[0103] In S3, the difference between the three-phase circulating current and the circulating current reference value is input into a second proportional resonant controller, and a second transfer function in the second proportional resonant controller is used to output an internal unbalanced voltage drop reference value of the negative sequence three-phase.

[0104] The second transfer function is determined based on the proportional link gain of the double frequency circulating current, the resonant gain of the secondary resonant controller and the bandwidth of the secondary resonant controller.

[0105] It should be noted that the second transfer function includes the following calculation formula:

[0106]

[0107] Among them, K p2 is the proportional gain of the double frequency circulating current, K i2 is the resonant gain of the secondary resonant controller, ω c2 is the bandwidth of the secondary resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, G PR2 (s) is the second transfer function, u cirj_ref It is the reference value of internal unbalanced voltage drop of negative sequence three phases.

[0108] For example, Figure 5 A schematic diagram of a double frequency circulating current suppression strategy provided by the present invention, such as Figure 5 As shown, the three-phase bridge arm current i pj and i nj Add and divide by 2 to get the three-phase circulating current i cirj , without coordinate transformation, the three-phase circulating current i cirj and the circulating current reference value i cir_ref (When the circulating current is suppressed, the reference value is 0; when the circulating current is injected, the reference value is the expected value) After subtraction, the proportional resonance (PR) controller GPR2 (s), directly obtain the internal unbalanced voltage drop reference value u of the negative sequence three-phase cirj_ref .

[0109] Embodiment 2:

[0110] Based on the same inventive concept, Figure 6 A block diagram of a DC current-based power transmission harmonic suppression system provided by the present invention, such as Figure 6 As shown, the system may include:

[0111] A parameter acquisition unit 601 is used to acquire a DC current of a voltage source converter in a hybrid cascade DC power transmission system, an internal unbalanced voltage drop reference value of a negative sequence three-phase, and a modulation wave controlled and issued by the voltage source converter, wherein the negative sequence three-phase is a negative sequence component of a circulating current in the voltage source converter in the hybrid cascade DC power transmission system;

[0112] A harmonic voltage component determination unit 602, configured to perform commutation suppression control processing on the DC current of the voltage source converter by using a low-pass filter and a first proportional resonant controller to obtain a harmonic voltage component of the voltage source converter;

[0113] An actual modulation wave determination unit 603 is used to calculate the actual modulation wave of the voltage source converter based on the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave sent by the voltage source converter control and the harmonic voltage component;

[0114] The control unit 604 is used to control the voltage source converter based on the actual modulation wave of the voltage source converter.

[0115] Optionally, the harmonic voltage component determining unit 602 is specifically configured to:

[0116] Based on the direct current of the voltage source converter, outputting the fluctuation amount of the direct current by using a low-pass filter;

[0117] The fluctuation amount of the DC current is input into a first proportional resonant controller, and the first transfer function in the first proportional resonant controller is used to output the harmonic voltage component of the voltage source converter, wherein the first transfer function is determined based on the proportional link gain, the resonant gain and bandwidth of the sixth resonant controller, and the resonant gain and bandwidth of the twelfth resonant controller.

[0118] Optionally, the first transfer function includes the following calculation formula:

[0119]

[0120] Among them, K p1 is the proportional link gain, K i6is the resonant gain of the sixth resonant controller, K i12 is the resonant gain of the twelve-order resonant controller, ω c6 is the bandwidth of the sixth resonant controller, ω c12 is the bandwidth of the twelve-order resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, G PR1 (s) is the first transfer function, ΔU dump is the harmonic voltage component of the voltage source converter.

[0121] Optionally, the system may further include: an unbalanced voltage drop reference value acquisition unit; the unbalanced voltage drop reference value acquisition unit is used to:

[0122] Obtaining a three-phase bridge arm current of the voltage source converter;

[0123] Taking the average value of the upper bridge arm current and the lower bridge arm current in the three-phase bridge arm current of the voltage source converter as the three-phase circulating current of the voltage source converter;

[0124] The difference between the three-phase circulating current and the circulating current reference value is input into a second proportional resonant controller, and the internal unbalanced voltage drop reference value of the negative-sequence three-phase is outputted using a second transfer function in the second proportional resonant controller, wherein the second transfer function is determined based on the proportional link gain of the doubled frequency circulating current, the resonant gain of the secondary resonant controller and the bandwidth of the secondary resonant controller.

[0125] Optionally, the second transfer function includes the following calculation formula:

[0126]

[0127] Among them, K p2 is the proportional gain of the double frequency circulating current, K i2 is the resonant gain of the secondary resonant controller, ω c2 is the bandwidth of the secondary resonant controller, ω 0 is the power frequency angular frequency, s is a complex variable, G PR2 (s) is the second transfer function, u cirj_ref It is the reference value of internal unbalanced voltage drop of negative sequence three phases.

[0128] Optionally, the actual modulation wave determining unit 603 is specifically configured to:

[0129] Calculating a first difference between an internal unbalanced voltage drop reference value of the negative-sequence three-phase and a modulation wave controlled by the voltage source converter;

[0130] Subtracting the first difference from the harmonic voltage component to obtain a second difference;

[0131] The second difference is used as the actual modulation wave of the voltage source converter.

[0132] Optionally, the control unit 604 is specifically configured to:

[0133] By outputting the actual modulation wave to the voltage source converter, the output current of the voltage source converter is controlled.

[0134] Embodiment 3:

[0135] Based on the same inventive concept, the present invention also provides a computer device, such as Figure 7 As shown, the computer device includes a processor and a memory, the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits, or other processors.

[0136] (Application Specific Integrated Circuit, ASIC), off-the-shelf programmable gate array (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, and are suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in a computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the power transmission harmonic suppression method based on DC current in the above-mentioned embodiment.

[0137] Embodiment 4:

[0138] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the power transmission harmonic suppression method based on DC current in the above embodiment.

[0139] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0140] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0141] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1A function specified in one or more boxes.

[0142] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0143] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A method for suppressing power transmission harmonics based on direct current, characterized in that: The method comprises: Obtaining a DC current of a voltage source converter in a hybrid cascade DC power transmission system, an internal unbalanced voltage drop reference value of a negative sequence three-phase, and a modulation wave controlled and sent by the voltage source converter, wherein the negative sequence three-phase is a negative sequence component of a circulating current in the voltage source converter in the hybrid cascade DC power transmission system; Using a low-pass filter and a first proportional resonant controller to perform commutation suppression control processing on the DC current of the voltage source converter to obtain a harmonic voltage component of the voltage source converter; Based on the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave sent by the voltage source converter control and the harmonic voltage component, the actual modulation wave of the voltage source converter is calculated; The voltage source converter is controlled based on the actual modulation wave of the voltage source converter.

2. The method according to claim 1, characterized in that The method of performing commutation suppression control processing on the DC current of the voltage source converter by using a low-pass filter and a first proportional resonant controller to obtain the harmonic voltage component of the voltage source converter includes: Based on the direct current of the voltage source converter, outputting the fluctuation amount of the direct current by using a low-pass filter; The fluctuation amount of the DC current is input into a first proportional resonant controller, and the first transfer function in the first proportional resonant controller is used to output the harmonic voltage component of the voltage source converter, wherein the first transfer function is determined based on the proportional link gain, the resonant gain and bandwidth of the sixth resonant controller, and the resonant gain and bandwidth of the twelfth resonant controller.

3. The method according to claim 2, characterized in that The first transfer function includes the following calculation formula: Among them, K p1 is the proportional link gain, K i6 is the resonant gain of the sixth resonant controller, K i12 is the resonant gain of the twelve-order resonant controller, ω c6 is the bandwidth of the sixth resonant controller, ω c12 is the bandwidth of the twelve-order resonant controller, ω0 is the power frequency angular frequency, s is a complex variable, G PR1 (s) is the first transfer function, ΔU dump is the harmonic voltage component of the voltage source converter.

4. The method according to claim 1, characterized in that The internal unbalanced voltage drop reference value of the negative sequence three-phase is obtained as follows: Obtaining a three-phase bridge arm current of the voltage source converter; Taking the average value of the upper bridge arm current and the lower bridge arm current in the three-phase bridge arm current of the voltage source converter as the three-phase circulating current of the voltage source converter; The difference between the three-phase circulating current and the circulating current reference value is input into a second proportional resonant controller, and the internal unbalanced voltage drop reference value of the negative-sequence three-phase is outputted using a second transfer function in the second proportional resonant controller, wherein the second transfer function is determined based on the proportional link gain of the doubled frequency circulating current, the resonant gain of the secondary resonant controller and the bandwidth of the secondary resonant controller.

5. The method according to claim 4, characterized in that The second transfer function includes the following calculation formula: Among them, K p2 is the proportional gain of the double frequency circulating current, K i2 is the resonant gain of the secondary resonant controller, ω c2 is the bandwidth of the secondary resonant controller, ω0 is the power frequency angular frequency, s is a complex variable, G PR2 (s) is the second transfer function, u cirj_ref It is the reference value of internal unbalanced voltage drop of negative sequence three phases.

6. The method according to claim 1, characterized in that The actual modulation wave of the voltage source converter is calculated based on the internal unbalanced voltage drop reference value of the negative sequence three-phase, the modulation wave sent by the voltage source converter control and the harmonic voltage component, including: Calculating a first difference between an internal unbalanced voltage drop reference value of the negative-sequence three-phase and a modulation wave controlled by the voltage source converter; Subtracting the first difference from the harmonic voltage component to obtain a second difference; The second difference is used as the actual modulation wave of the voltage source converter.

7. The method according to claim 1, characterized in that The controlling the voltage source converter based on the actual modulation wave of the voltage source converter comprises: By outputting the actual modulation wave to the voltage source converter, the output current of the voltage source converter is controlled.

8. A power transmission harmonic suppression system based on direct current, characterized in that: The system comprises: A parameter acquisition unit, used for acquiring a DC current of a voltage source converter in a hybrid cascade DC power transmission system, an internal unbalanced voltage drop reference value of a negative sequence three-phase, and a modulation wave controlled and issued by the voltage source converter, wherein the negative sequence three-phase is a negative sequence component of a circulating current in the voltage source converter in the hybrid cascade DC power transmission system; a harmonic voltage component determination unit, configured to perform commutation suppression control processing on the DC current of the voltage source converter by using a low-pass filter and a first proportional resonant controller to obtain a harmonic voltage component of the voltage source converter; An actual modulation wave determination unit, configured to calculate an actual modulation wave of the voltage source converter based on an internal unbalanced voltage drop reference value of the negative sequence three-phase, a modulation wave controlled by the voltage source converter, and the harmonic voltage component; A control unit is used to control the voltage source converter based on an actual modulation wave of the voltage source converter.

9. The system according to claim 8, characterized in that The harmonic voltage component determination unit is specifically used to: Based on the direct current of the voltage source converter, outputting the fluctuation amount of the direct current by using a low-pass filter; The fluctuation amount of the DC current is input into a first proportional resonant controller, and the first transfer function in the first proportional resonant controller is used to output the harmonic voltage component of the voltage source converter, wherein the first transfer function is determined based on the proportional link gain, the resonant gain and bandwidth of the sixth resonant controller, and the resonant gain and bandwidth of the twelfth resonant controller.

10. The system according to claim 9, characterized in that The first transfer function includes the following calculation formula: Among them, K p1 is the proportional link gain, K i6 is the resonant gain of the sixth resonant controller, K i12 is the resonant gain of the twelve-order resonant controller, ω c6 is the bandwidth of the sixth resonant controller, ω c12 is the bandwidth of the twelve-order resonant controller, ω0 is the power frequency angular frequency, s is a complex variable, G PR1 (s) is the first transfer function, ΔU dump is the harmonic voltage component of the voltage source converter.

11. The system according to claim 8, characterized in that The system further comprises: an unbalanced voltage drop reference value obtaining unit; the unbalanced voltage drop reference value obtaining unit is used to: Obtaining a three-phase bridge arm current of the voltage source converter; Taking the average value of the upper bridge arm current and the lower bridge arm current in the three-phase bridge arm current of the voltage source converter as the three-phase circulating current of the voltage source converter; The difference between the three-phase circulating current and the circulating current reference value is input into a second proportional resonant controller, and the internal unbalanced voltage drop reference value of the negative-sequence three-phase is outputted using a second transfer function in the second proportional resonant controller, wherein the second transfer function is determined based on the proportional link gain of the doubled frequency circulating current, the resonant gain of the secondary resonant controller and the bandwidth of the secondary resonant controller.

12. The system according to claim 11, characterized in that The second transfer function includes the following calculation formula: Among them, K p2 is the proportional gain of the double frequency circulating current, K i2 is the resonant gain of the secondary resonant controller, ω c2 is the bandwidth of the secondary resonant controller, ω0 is the power frequency angular frequency, s is a complex variable, G PR2 (s) is the second transfer function, u cirj_ref It is the reference value of internal unbalanced voltage drop of negative sequence three phases.

13. The system according to claim 8, characterized in that The actual modulation wave determination unit is specifically used for: Calculating a first difference between an internal unbalanced voltage drop reference value of the negative-sequence three-phase and a modulation wave controlled by the voltage source converter; Subtracting the first difference from the harmonic voltage component to obtain a second difference; The second difference is used as the actual modulation wave of the voltage source converter.

14. The system according to claim 8, characterized in that The control unit is specifically used for: By outputting the actual modulation wave to the voltage source converter, the output current of the voltage source converter is controlled.

15. A computer device, characterized in that: include: one or more processors; The processor is used to store one or more programs; When the one or more programs are executed by the one or more processors, the direct current-based power transmission harmonic suppression method as claimed in any one of claims 1 to 7 is implemented.

16. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, the method for suppressing power transmission harmonics based on direct current as described in any one of claims 1 to 7 is implemented.

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