Converter phase-to-phase voltage equalization control method and device and converter

Abstract

The application relates to a converter phase-to-phase voltage-sharing control method and device and a converter. First, three-phase alternating-current voltages, three-phase output currents and three-phase direct-current voltages of the converter are acquired, based on which, a negative sequence current injection weight and a zero sequence voltage injection weight are determined in real time, and combined with a full injection amount required by a single negative sequence current strategy and a full injection amount required by a single zero sequence voltage strategy, a final negative sequence current instruction and a zero sequence voltage instruction are generated, and the converter is driven to operate. When the grid voltage is greatly asymmetrically dropped, the efficiency of the negative sequence current strategy is reduced, the weight is automatically reduced, and voltage-sharing failure is avoided; under a light load condition, the efficiency of the zero sequence voltage strategy is reduced, and the weight is also automatically reduced, so that over-modulation is prevented. Weighted distribution makes the total injection amount minimum, phase-to-phase voltage-sharing is realized at the minimum injection cost, and therefore the voltage-sharing effect is significantly improved under all conditions.

Description

Technical Field

[0001] This application relates to the field of converter technology, and in particular to a converter phase-to-phase pressure equalization control method, device and converter. Background Technology

[0002] With the rapid development of science and technology, cascaded converters of various types, such as modular commutated converters (MCC), modular multilevel converters (MMC), and star-chain converters (STATCOM), have been widely used in medium and high voltage power conversion due to their advantages such as modular structure, ease of expansion, and low harmonic content in output voltage. Under grid voltage asymmetry conditions, the DC-side voltage of each phase submodule in a cascaded converter will become unbalanced. If left uncontrolled, this will lead to the converter malfunctioning or even being damaged.

[0003] Currently, common methods for achieving phase-to-phase voltage equalization control in converters include negative-sequence current injection, zero-sequence voltage injection, and hardware switching control. However, the negative-sequence current injection strategy has insufficient regulation capability when the grid voltage drops significantly, and may even worsen the grid voltage imbalance; the zero-sequence voltage injection strategy has insufficient regulation capability under light load conditions and is prone to over-regulation; and hardware control relies on preset thresholds, which can easily lead to frequent strategy switching. Therefore, phase-to-phase voltage equalization schemes in converters suffer from poor voltage equalization performance. Summary of the Invention

[0004] Therefore, it is necessary to address the problem of poor pressure equalization effect of the phase-to-phase pressure equalization scheme in converters by proposing a converter phase-to-phase pressure equalization control method, device, and converter.

[0005] This application provides a method for phase-to-phase voltage equalization control of a converter. The method includes: acquiring the three-phase AC voltage and three-phase output current on the AC grid side of the converter, and the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter; determining, based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current, a negative-sequence current injection weight, a zero-sequence voltage injection weight, and the full negative-sequence current injection amount required for a single negative-sequence current injection strategy and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy; wherein the sum of the negative-sequence current injection weight and the zero-sequence voltage injection weight is 1; determining a negative-sequence current command based on the negative-sequence current injection weight and the full negative-sequence current injection amount, and determining a zero-sequence voltage command based on the zero-sequence voltage injection weight and the full zero-sequence voltage injection amount; generating a drive signal based on the negative-sequence current command and the zero-sequence voltage command; the drive signal is used to drive the converter circuit of the converter to operate.

[0006] In one embodiment, determining the negative-sequence current injection weight, the zero-sequence voltage injection weight, and the full negative-sequence current injection amount required for a single negative-sequence current injection strategy and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current includes: extracting the positive-sequence voltage dq-axis component, the negative-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current; and extracting the positive-sequence voltage dq-axis component, the negative-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current; and extracting the negative-sequence current ... and the negative-sequence current dq-axis component based on the three-phase AC voltage, the three-phase DC voltage, and the positive-sequence current dq-axis component, the negative-sequence current An imbalance analysis is performed on the dq-axis components of the voltage, the negative-sequence voltage, the positive-sequence current, and the negative-sequence current to determine the three-phase unbalanced power. Based on the three-phase unbalanced power, the positive-sequence voltage, the positive-sequence current, and the negative-sequence current, the full-scale negative-sequence current injection required for a single negative-sequence current injection strategy and the full-scale zero-sequence voltage injection required for a single zero-sequence voltage injection strategy are determined. Based on the three-phase unbalanced power, the negative-sequence current injection weight and the zero-sequence voltage injection weight are determined.

[0007] In one embodiment, the step of performing unbalance analysis based on the three-phase DC voltage, the positive-sequence voltage dq-axis component, the negative-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component to determine the three-phase unbalanced power includes: determining the three-phase average value of the three-phase DC voltage; determining the first three-phase unbalanced power caused by the three-phase DC voltage deviation based on the three-phase DC voltage and the three-phase average value; determining the second three-phase unbalanced power caused by the interaction of negative-sequence voltage and positive-sequence current based on the negative-sequence voltage dq-axis component and the positive-sequence current dq-axis component; and determining the third three-phase unbalanced power caused by the interaction of positive-sequence voltage and negative-sequence current based on the positive-sequence voltage dq-axis component and the negative-sequence current dq-axis component.

[0008] In one embodiment, determining the full negative-sequence current injection amount required for a single negative-sequence current injection strategy and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy based on the three-phase unbalanced power, the positive-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component includes: determining the full negative-sequence current injection amount required for a single negative-sequence current injection strategy based on the first three-phase unbalanced power, the second three-phase unbalanced power, and the positive-sequence voltage dq-axis component; and determining the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy based on the first three-phase unbalanced power, the second three-phase unbalanced power, the third three-phase unbalanced power, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component.

[0009] In one embodiment, determining the negative-sequence current injection weight and the zero-sequence voltage injection weight based on the three-phase unbalanced power includes: separating the positive and negative sequences based on the three-phase AC voltage and the three-phase output current to determine the positive-sequence voltage amplitude, the negative-sequence voltage amplitude, and the positive-sequence current amplitude; determining the negative-sequence current strategy capability coefficient and the zero-sequence voltage strategy capability coefficient based on the positive-sequence voltage amplitude, the negative-sequence voltage amplitude, and the positive-sequence current amplitude; and determining the negative-sequence current injection weight and the zero-sequence voltage injection weight based on the negative-sequence current strategy capability coefficient, the zero-sequence voltage strategy capability coefficient, and the three-phase unbalanced power.

[0010] In one embodiment, determining the negative-sequence current injection weight and the zero-sequence voltage injection weight based on the negative-sequence current strategy capability coefficient, the zero-sequence voltage strategy capability coefficient, and the three-phase unbalanced power includes: determining the initial negative-sequence current injection weight and the initial zero-sequence voltage injection weight based on the negative-sequence current strategy capability coefficient, the zero-sequence voltage strategy capability coefficient, and the three-phase unbalanced power; and performing filtering processing based on the initial negative-sequence current injection weight and the initial zero-sequence voltage injection weight to obtain the negative-sequence current injection weight and the zero-sequence voltage injection weight.

[0011] In one embodiment, the method further includes: obtaining the sum of the first-phase unbalanced power, the sum of the second-phase unbalanced power, and the sum of the third-phase unbalanced power based on the three-phase unbalanced power, and determining the maximum unbalanced power sum; if the maximum unbalanced power sum is greater than a preset power threshold, then performing the step of determining the negative-sequence current injection weight and the zero-sequence voltage injection weight based on the three-phase unbalanced power; if the maximum unbalanced power sum is less than or equal to the preset power threshold, then configuring the zero-sequence voltage injection weight to 0 and the negative-sequence current injection weight to 1.

[0012] In one embodiment, generating a drive signal based on the negative-sequence current command and the zero-sequence voltage command includes: performing amplitude limiting processing on the negative-sequence current command and the zero-sequence voltage command to obtain a target negative-sequence current command and a target zero-sequence voltage command; and generating a drive signal based on the target negative-sequence current command and the target zero-sequence voltage command.

[0013] This application provides a converter phase-to-phase voltage equalization control device, the device comprising: a parameter acquisition module for acquiring the three-phase AC voltage and three-phase output current on the AC grid side of the converter, and the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter; a weight analysis module for determining, based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current, the negative-sequence current injection weight, the zero-sequence voltage injection weight, and the full negative-sequence current injection amount required for a single negative-sequence current injection strategy, and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy; wherein the sum of the negative-sequence current injection weight and the zero-sequence voltage injection weight is 1; an instruction generation module for determining, based on the negative-sequence current injection weight and the full negative-sequence current injection amount, a negative-sequence current instruction, and a zero-sequence voltage instruction; and a drive control module for generating a drive signal based on the negative-sequence current instruction and the zero-sequence voltage instruction; the drive signal is used to drive the converter circuit of the converter to operate.

[0014] This application provides a converter including a connected converter circuit and a controller, the controller being used to perform the steps of the above method.

[0015] The aforementioned converter phase-to-phase voltage equalization control method, device, and converter first acquire the three-phase AC voltage, three-phase output current, and three-phase DC voltage of the converter. Based on this, the negative-sequence current injection weight and zero-sequence voltage injection weight (the sum of the two is 1) are determined in real time. These are then combined with the full injection amount required for a single negative-sequence current strategy and the full injection amount required for a single zero-sequence voltage strategy to generate the final negative-sequence current command and zero-sequence voltage command, thereby driving the converter operation. This method abandons the traditional hard switching mode of two-way selection or linear interpolation, realizing the coordinated weighted allocation of two voltage equalization strategies. The sum of the weights being 1 ensures the physical consistency of the control command, while the weights themselves are dynamically calculated based on real-time operating conditions (i.e., positive-sequence voltage, negative-sequence voltage, positive-sequence current, negative-sequence current, etc.), automatically obtaining a higher contribution according to the actual scenario. Thus, when the grid voltage drops significantly asymmetrically, the efficiency of the negative-sequence current strategy decreases, and its weight automatically decreases to avoid voltage equalization failure; similarly, under light load conditions, the efficiency of the zero-sequence voltage strategy decreases, and its weight also automatically decreases to prevent overmodulation. Meanwhile, the weighted allocation minimizes the total injection amount (the weighted sum of negative sequence current and zero sequence voltage), achieving phase-to-phase voltage equalization with minimal injection cost, thereby significantly improving the voltage equalization effect under all operating conditions. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of a converter phase-to-phase pressure equalization control method in one embodiment of this application;

[0018] Figure 2 This is a schematic diagram of the weight analysis process in one embodiment of this application;

[0019] Figure 3 This is a schematic diagram of a three-phase unbalanced power analysis process in one embodiment of this application;

[0020] Figure 4 This is a schematic diagram of the first three-phase unbalanced power calculation logic in one embodiment of this application;

[0021] Figure 5 This is a schematic diagram of the weight calculation process in one embodiment of this application;

[0022] Figure 6 This is a schematic diagram of the weight calculation process in another embodiment of this application;

[0023] Figure 7 This is a schematic flowchart of a converter phase-to-phase pressure equalization control method in another embodiment of this application;

[0024] Figure 8 This is a schematic diagram of the converter phase-to-phase pressure equalization control device in one embodiment of this application. Detailed Implementation

[0025] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0026] The phase-to-phase voltage equalization control for converters provided in this application is applicable to cascaded converters, such as modular commutated converters (MCC), modular multilevel converters (MMC), and star-chain converters (STATCOM), etc., without specific limitations; selection can be based on actual needs. The converters in this application can be used for AC / DC power transmission, as well as in energy storage systems, integrated photovoltaic-energy storage systems, or grid-connected energy storage systems, again without limitations.

[0027] Please see Figure 1 This application provides a converter phase-to-phase pressure equalization control method, which includes steps 102, 104, 106 and 108.

[0028] Step 102: Obtain the three-phase AC voltage and three-phase output current on the AC grid side of the converter, as well as the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter.

[0029] A converter refers to a cascaded converter, which includes a three-phase switched capacitor bridge submodule used to achieve AC-DC power conversion. Phase-to-phase voltage equalization control refers to the control objective of maintaining a balanced three-phase DC voltage in the converter by adjusting the injected current or voltage. Three-phase AC voltage refers to the instantaneous voltage values ​​of phases A, B, and C collected from the AC grid side of the converter. Three-phase output current refers to the instantaneous output current values ​​of phases A, B, and C collected from the AC grid side of the converter. Three-phase DC voltage refers to the DC-side voltage of each of the three-phase switched capacitor bridge submodules (A, B, and C) in the converter.

[0030] It is understood that there is no single way to obtain the three-phase AC voltage, three-phase output current and three-phase DC voltage. In one embodiment, a voltage acquisition device or other device can be configured at the corresponding position of the converter to send the acquisition results to the controller in real time or periodically.

[0031] Step 104: Based on the three-phase AC voltage, three-phase DC voltage, and three-phase output current, determine the negative sequence current injection weight, the zero sequence voltage injection weight, and the full negative sequence current injection amount required by the single negative sequence current injection strategy and the full zero sequence voltage injection amount required by the single zero sequence voltage injection strategy.

[0032] The sum of the negative-sequence current injection weight and the zero-sequence voltage injection weight is 1. The negative-sequence current injection weight is a coefficient used to quantify the contribution of the negative-sequence current injection strategy to the coordinated control. The zero-sequence voltage injection weight is a coefficient used to quantify the contribution of the zero-sequence voltage injection strategy to the coordinated control. The full negative-sequence current injection amount refers to the complete d-axis and q-axis command values ​​of the negative-sequence current required to offset the current three-phase unbalanced power when only the negative-sequence current injection strategy is used and no weight is set. The full zero-sequence voltage injection amount refers to the complete d-axis and q-axis command values ​​of the zero-sequence voltage required to offset the current three-phase unbalanced power when only the zero-sequence voltage injection strategy is used and no weight is set.

[0033] This method first collects three-phase AC voltage and three-phase output current from the AC grid side of the converter, and simultaneously collects three-phase DC voltage from the three-phase switched capacitor bridge module. Based on this real-time data, the controller calculates two weighting coefficients: the negative-sequence current injection weight and the zero-sequence voltage injection weight, which are added together to equal 1. Furthermore, the controller also calculates the full negative-sequence current injection amount required when using only the negative-sequence current strategy, and the full zero-sequence voltage injection amount required when using only the zero-sequence voltage strategy.

[0034] Step 106: Determine the negative sequence current command based on the negative sequence current injection weight and the full negative sequence current injection amount, and determine the zero sequence voltage command based on the zero sequence voltage injection weight and the full zero sequence voltage injection amount.

[0035] The negative sequence current command is the final d-axis and q-axis reference value of the negative sequence current, obtained by multiplying the negative sequence current injection weight by the full negative sequence current injection amount. The zero sequence voltage command is the final d-axis and q-axis reference value of the zero sequence voltage, obtained by multiplying the zero sequence voltage injection weight by the full zero sequence voltage injection amount.

[0036] After obtaining the above parameters, the controller multiplies the full-scale negative-sequence current injection amount by the negative-sequence current injection weight to obtain the final negative-sequence current command, and multiplies the full-scale zero-sequence voltage injection amount by the zero-sequence voltage injection weight to obtain the final zero-sequence voltage command.

[0037] Step 108: Generate a drive signal based on the negative sequence current command and the zero sequence voltage command.

[0038] The drive signal is used to drive the converter circuit of the converter. The drive signal refers to the switching signal generated by modulation through methods such as PWM (Pulse Width Modulation), which is used to control the on and off of the power switching devices in the converter circuit within the converter.

[0039] After receiving the negative sequence current command and the zero sequence voltage command, the controller can send the negative sequence current command into the inner current loop and superimpose the zero sequence voltage command onto the three-phase modulation wave. Finally, the drive signal is obtained through PWM modulation, thereby controlling the on and off of the power switching devices to achieve phase-to-phase voltage regulation, that is, phase-to-phase voltage equalization of the converter.

[0040] The aforementioned converter phase-to-phase voltage equalization control method first acquires the three-phase AC voltage, three-phase output current, and three-phase DC voltage of the converter. Based on this, it determines the negative-sequence current injection weight and the zero-sequence voltage injection weight (the sum of which is 1) in real time. These weights are then combined with the full injection amounts required for a single negative-sequence current strategy and a single zero-sequence voltage strategy, respectively, to generate the final negative-sequence current command and zero-sequence voltage command, thereby driving the converter operation. This method abandons the traditional hard-switching mode of two-way selection or linear interpolation, achieving a coordinated weighted allocation of the two voltage equalization strategies. The sum of the weights being 1 ensures the physical consistency of the control commands, while the weights themselves are dynamically calculated based on real-time operating conditions (i.e., positive-sequence voltage, negative-sequence voltage, positive-sequence current, negative-sequence current, etc.), automatically obtaining a higher contribution according to the actual scenario. Thus, when the grid voltage drops significantly asymmetrically, the efficiency of the negative-sequence current strategy decreases, and its weight automatically decreases to avoid voltage equalization failure; similarly, under light load conditions, the efficiency of the zero-sequence voltage strategy decreases, and its weight also automatically decreases to prevent overmodulation. Meanwhile, the weighted allocation minimizes the total injection amount (the weighted sum of negative sequence current and zero sequence voltage), achieving phase-to-phase voltage equalization with minimal injection cost, thereby significantly improving the voltage equalization effect under all operating conditions.

[0041] Please see Figure 2 In one embodiment, step 104 includes steps 201, 202, 203 and 204.

[0042] Step 201: Extract the positive sequence voltage dq-axis component, negative sequence voltage dq-axis component, positive sequence current dq-axis component, and negative sequence current dq-axis component based on the three-phase AC voltage and three-phase output current.

[0043] Step 202: Perform an unbalance analysis based on the three-phase DC voltage, the positive-sequence voltage dq-axis component, the negative-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component to determine the three-phase unbalanced power.

[0044] Step 203: Based on the three-phase unbalanced power, the positive sequence voltage dq-axis component, the positive sequence current dq-axis component, and the negative sequence current dq-axis component, determine the full amount of negative sequence current injection required by the single negative sequence current injection strategy and the full amount of zero sequence voltage injection required by the single zero sequence voltage injection strategy.

[0045] Step 204: Determine the negative sequence current injection weight and the zero sequence voltage injection weight based on the three-phase unbalanced power.

[0046] The positive-sequence voltage dq-axis component refers to the components of the positive-sequence voltage on the d and q axes obtained after separating the positive and negative sequences of the three-phase AC voltage and then performing a synchronous rotating coordinate transformation (i.e., dq transformation). It includes the positive-sequence voltage d-axis component u. pd Positive sequence voltage q-axis component u pqThe negative sequence voltage dq-axis components are obtained by separating the three-phase AC voltage into positive and negative sequences, followed by synchronous rotating coordinate transformation, resulting in the negative sequence voltage components on the d and q axes. These components include the negative sequence voltage d-axis component u. nd Negative sequence voltage q-axis component u nq .

[0047] The positive sequence current dq-axis component refers to the components of the positive sequence current on the d-axis and q-axis obtained after the three-phase output current has undergone positive and negative sequence separation and dq transformation. It includes the positive sequence current d-axis component i. pd Positive sequence current q-axis component i pq The positive-sequence current dq-axis component refers to the components of the negative-sequence current on the d and q axes obtained after the three-phase output current has undergone positive-negative sequence separation and dq transformation, including the negative-sequence current d-axis component i. nd negative sequence current q-axis component i nq Three-phase unbalanced power refers to the power change caused by three-phase imbalance. Generally speaking, it should include three categories: the first three-phase unbalanced power caused by the deviation of three-phase DC voltage, the second three-phase unbalanced power caused by the action of negative sequence voltage and positive sequence current, and the third three-phase unbalanced power caused by the action of positive sequence voltage and negative sequence current.

[0048] This embodiment further refines the processing of three-phase AC voltage and three-phase output current. First, through positive and negative sequence separation and dq transformation, the positive-sequence voltage dq-axis components, negative-sequence voltage dq-axis components, positive-sequence current dq-axis components, and negative-sequence current dq-axis components are extracted. Then, combined with the three-phase DC voltage, unbalanced power analysis is performed on these dq-axis components to calculate the three-phase unbalanced power in the current system. Based on this three-phase unbalanced power, and combining the positive-sequence voltage dq-axis components, the full-scale negative-sequence current injection required for a single negative-sequence current injection strategy, and the full-scale zero-sequence voltage injection required for a single zero-sequence voltage injection strategy, are calculated respectively. Simultaneously, based on the numerical characteristics of the three-phase unbalanced power, the negative-sequence current injection weight and the zero-sequence voltage injection weight are calculated.

[0049] The above scheme extracts the positive and negative sequence dq-axis components and performs three-phase unbalanced power analysis. Then, it calculates the full injection amount of negative sequence current and zero sequence voltage, providing a physically clear power benchmark for subsequent weight allocation. This shifts voltage equalization control from experience-based or threshold switching to quantitative calculation based on real-time unbalanced power, thereby accurately matching the actual power compensation required, avoiding over-injection or under-injection, and fundamentally improving voltage equalization accuracy.

[0050] Please see Figure 3 In one embodiment, step 202 includes steps 301, 302, 303 and 304.

[0051] Step 301: Determine the three-phase average value of the three-phase DC voltage.

[0052] Step 302: Determine the first three-phase unbalanced power caused by the three-phase DC voltage deviation based on the three-phase DC voltage and the three-phase average value.

[0053] Step 303: Determine the second-third phase unbalanced power caused by the interaction of negative-sequence voltage and positive-sequence current based on the dq-axis components of negative-sequence voltage and positive-sequence current.

[0054] Step 304: Determine the third three-phase unbalanced power caused by the interaction of positive sequence voltage and negative sequence current based on the dq-axis components of positive sequence voltage and negative sequence current.

[0055] The three-phase average value refers to the average value of the DC voltage of the three individual phases in a three-phase DC voltage. The first three-phase unbalanced power caused by the deviation of the three-phase DC voltage refers to the three-phase power value obtained by PI (proportional-integral) regulation after the deviation between the DC voltage of each phase and the three-phase average value. It represents the active power that needs to be regulated to maintain the balance of the DC voltage of each phase.

[0056] The second- and third-phase unbalanced power caused by the interaction of negative-sequence voltage and positive-sequence current is the power of each phase calculated from the dq-axis components of the negative-sequence voltage and the positive-sequence current according to instantaneous power theory. It is the intrinsic unbalanced disturbance caused by asymmetrical faults in the power grid. The third-phase unbalanced power caused by the interaction of positive-sequence voltage and negative-sequence current is the power generated by the injected negative-sequence current and positive-sequence voltage acting on each phase. It is the controllable component used by the negative-sequence current injection strategy to actively adjust the power distribution between phases.

[0057] For example, in one embodiment, the method for determining the first three-phase unbalanced power can be found in [reference needed]. Figure 4 ,in, This represents the first three-phase unbalanced power corresponding to A. This represents the first three-phase unbalanced power corresponding to B. This represents the first three-phase unbalanced power corresponding to C; , and These represent the DC voltages corresponding to phases A, B, and C in a three-phase DC voltage system. This represents the three-phase average value, which is essentially... , and The average of the three.

[0058] In one embodiment, according to instantaneous power theory, the unbalanced power of the second and third phases caused by the interaction of negative-sequence voltage and positive-sequence current can be expressed as:

[0059]

[0060] in, This represents the unbalanced power of the second and third phases corresponding to A. This represents the unbalanced power of the second and third phases corresponding to B. This indicates the second and third phase unbalanced power corresponding to C; This represents the d-axis component of the positive sequence current. This represents the q-axis component of the positive sequence current. This represents the d-axis component of the negative sequence voltage. This represents the q-axis component of the negative sequence voltage.

[0061] In one embodiment, when a negative-sequence current is actively injected, the interaction between the positive-sequence voltage and the negative-sequence current also generates power, which is the third three-phase unbalanced power, and can be expressed as:

[0062]

[0063] in, This represents the third phase unbalanced power corresponding to A. This represents the third phase unbalanced power corresponding to B. This represents the third phase unbalanced power corresponding to C; This represents the d-axis component of the negative sequence current. This represents the q-axis component of the negative sequence current. This represents the d-axis component of the positive sequence voltage. This represents the q-axis component of the positive sequence voltage.

[0064] The above scheme decomposes the three-phase unbalanced power into three categories: those caused by DC voltage deviation, those caused by the interaction of negative sequence voltage and positive sequence current, and those caused by the interaction of positive sequence voltage and negative sequence current. This decomposition allows the subsequent injection quantity calculation to compensate for different disturbance sources separately, avoiding control errors caused by mixing unbalanced power with different physical mechanisms, thereby improving the physical consistency and stability of voltage equalization control.

[0065] In one embodiment, step 203 includes: determining the full negative sequence current injection amount required for a single negative sequence current injection strategy based on the first three-phase unbalanced power, the second three-phase unbalanced power, and the positive sequence voltage dq-axis component; and determining the full zero sequence voltage injection amount required for a single zero sequence voltage injection strategy based on the first three-phase unbalanced power, the second three-phase unbalanced power, the third three-phase unbalanced power, and the positive sequence current dq-axis component and the negative sequence current dq-axis component.

[0066] In this embodiment, different power combinations are used to calculate the full injection amount for both the negative-sequence current injection strategy and the zero-sequence voltage injection strategy. For the negative-sequence current injection strategy, only the first and second phase unbalanced power are used, combined with the dq-axis component of the positive-sequence voltage, to calculate the full injection amount of the negative-sequence current. This is because the negative-sequence current injection strategy mainly regulates power through the interaction between the positive-sequence voltage and the negative-sequence current it generates, and cannot directly utilize the third phase unbalanced power. For the zero-sequence voltage injection strategy, all three types of three-phase unbalanced power are used, and both the dq-axis components of the positive-sequence current and the dq-axis components of the negative-sequence current are combined to calculate the full injection amount of the zero-sequence voltage.

[0067] For example, in one embodiment, the calculation of the full-capacity negative-sequence current injection includes:

[0068]

[0069] in, and These represent the full-capacity negative-sequence current injection amount corresponding to the d-axis and the full-capacity negative-sequence current injection amount corresponding to the q-axis, respectively. Represents the d-axis component of the positive sequence voltage; , and The power that the injected negative sequence current needs to balance in the three phases is expressed as follows: , as well as , This represents the first three-phase unbalanced power corresponding to A. This represents the first three-phase unbalanced power corresponding to B. This represents the first three-phase unbalanced power corresponding to C; This represents the unbalanced power of the second and third phases corresponding to A. This represents the unbalanced power of the second and third phases corresponding to B. This represents the unbalanced power of the second and third phases corresponding to C.

[0070] For example, in one embodiment, the calculation of the full-scale zero-sequence voltage injection amount includes:

[0071]

[0072] in, and These represent the full-scale injection of zero-sequence voltage corresponding to the d-axis and the full-scale injection of zero-sequence voltage corresponding to the q-axis, respectively. This represents the d-axis component of the positive sequence current. This represents the q-axis component of the positive sequence current. This represents the d-axis component of the negative sequence current. This represents the q-axis component of the negative sequence current.

[0073] , and The power that the injected zero-sequence voltage needs to balance in the three phases is expressed as follows: , as well as ,in, This represents the first three-phase unbalanced power corresponding to A. This represents the first three-phase unbalanced power corresponding to B. This represents the first three-phase unbalanced power corresponding to C; This represents the unbalanced power of the second and third phases corresponding to A. This represents the unbalanced power of the second and third phases corresponding to B. This represents the second and third phase unbalanced power corresponding to C. This represents the third phase unbalanced power corresponding to A. This represents the third phase unbalanced power corresponding to B. This represents the third unbalanced power corresponding to phase C.

[0074] The above scheme calculates the full-capacity injection of negative-sequence current using the first and second phase unbalanced power and the dq-axis component of the positive-sequence voltage. It further calculates the full-capacity injection of zero-sequence voltage by combining the first, second, and third phase unbalanced power and the dq-axis components of both positive and negative-sequence currents. This separate calculation method, based on different strategies and component levels, ensures that the full-capacity injection of each strategy strictly corresponds to the power type it can adjust, avoiding coupling interference between strategies and providing a clean and independent input for subsequent weighted allocation.

[0075] Please see Figure 5 In one embodiment, step 204 includes steps 502, 504 and 506.

[0076] Step 502: Separate the positive and negative sequences based on the three-phase AC voltage and the three-phase output current, and determine the positive sequence voltage amplitude, negative sequence voltage amplitude, and positive sequence current amplitude.

[0077] Step 504: Determine the negative sequence current strategy capability coefficient and the zero sequence voltage strategy capability coefficient based on the positive sequence voltage amplitude, negative sequence voltage amplitude, and positive sequence current amplitude.

[0078] Step 506: Determine the negative sequence current injection weight and the zero sequence voltage injection weight based on the negative sequence current strategy capability coefficient, the zero sequence voltage strategy capability coefficient, and the three-phase unbalanced power.

[0079] Positive-sequence voltage amplitude refers to the amplitude (per-unit value) of the positive-sequence component separated from the three-phase AC voltage; negative-sequence voltage amplitude refers to the amplitude (also per-unit value) of the negative-sequence component separated from the three-phase AC voltage; positive-sequence current amplitude refers to the amplitude (also per-unit value) of the positive-sequence component separated from the three-phase output current. The negative-sequence current strategy capability coefficient reflects the regulation efficiency of the negative-sequence current injection strategy under the current operating conditions. The zero-sequence voltage strategy capability coefficient represents the regulation efficiency of the zero-sequence voltage injection strategy under the current operating conditions.

[0080] This embodiment separates the three-phase AC voltage and three-phase output current into positive and negative sequences, extracting the positive-sequence voltage amplitude, negative-sequence voltage amplitude, and positive-sequence current amplitude. Then, two capability coefficients are calculated based on these amplitudes. For example, in one embodiment, the calculation method for the negative-sequence current strategy capability coefficient can be expressed as follows: ,in, This represents the negative sequence current strategy capability coefficient. These are small positive real numbers, used to avoid the denominator being 0. Indicates the positive sequence voltage amplitude. This represents the magnitude of the negative sequence voltage. Based on this, the higher the positive sequence voltage and the lower the negative sequence voltage, the higher the regulating power efficiency generated by the negative sequence current injection; when a large asymmetric voltage drop occurs in the power grid, the negative sequence voltage increases sharply. The subsequent sharp decline reflects the physical fact that the negative sequence current strategy has failed.

[0081] For example, in one embodiment, the zero-sequence voltage strategy capability coefficient can be expressed as: ,in, This represents the zero-sequence voltage strategy capability coefficient. This represents the magnitude of the positive-sequence current. Based on this, the higher the regulation power efficiency generated by zero-sequence voltage injection, the smaller the positive-sequence current under light load conditions. The value decreases accordingly, reflecting the physical fact that the zero-sequence voltage strategy has failed.

[0082] In this embodiment, the weight allocation is no longer a fixed threshold switching, but a quantitative evaluation of the physical efficiency of the strategy based on real-time measurement values, thus achieving adaptive, threshold-free collaborative control.

[0083] The above scheme introduces a negative-sequence current strategy capability coefficient (based on the ratio of positive-sequence voltage to negative-sequence voltage) and a zero-sequence voltage strategy capability coefficient (based on the positive-sequence current amplitude), directly quantifying the physical regulation efficiency of the two strategies under the current operating conditions. When a significant asymmetrical voltage drop occurs in the grid, the increase in negative-sequence voltage causes the negative-sequence current capability coefficient to automatically decrease, and its weight is reduced accordingly, avoiding the allocation of regulation tasks to the failed strategy. Under light load conditions, the small positive-sequence current causes the zero-sequence voltage capability coefficient to decrease, similarly automatically reducing its weight.

[0084] Please see Figure 6 In one embodiment, step 506 includes steps 602 and 604.

[0085] Step 602: Determine the initial negative sequence current injection weight and the initial zero sequence voltage injection weight based on the negative sequence current strategy capability coefficient, the zero sequence voltage strategy capability coefficient, and the three-phase unbalanced power.

[0086] Step 604: Perform filtering based on the initial negative sequence current injection weight and the initial zero sequence voltage injection weight to obtain the negative sequence current injection weight and the zero sequence voltage injection weight.

[0087] The initial negative-sequence current injection weight refers to the unfiltered weight value directly calculated from the aforementioned capacity coefficient and three-phase unbalanced power. The initial zero-sequence voltage injection weight represents the unfiltered zero-sequence voltage injection weight value. Filtering is achieved by smoothing the initial weights using a first-order low-pass filter.

[0088] For example, in one embodiment, since the sum of the two weights is 1, only one weight needs to be calculated, and the other weight can be calculated directly. Specifically:

[0089]

[0090]

[0091] in, Characterizing the sum of the maximum three-phase unbalanced power that the negative-sequence current injection strategy can provide, for example, in one embodiment, it can be expressed as: ; The sum of the maximum three-phase unbalanced power that can be provided by the zero-sequence voltage injection strategy can be represented in one embodiment as follows: ; It can also be understood as a tiny positive real number.

[0092] In this embodiment, the sum of the two weights is 1, which respectively represent the contribution weights of the two strategies in the cooperative control. This weight allocation method ensures that even if the capability coefficient of a certain strategy is high, its weight will be automatically reduced if its maximum power is limited by hardware constraints, thereby avoiding incorrect allocation.

[0093] For example, in one embodiment, a first-order low-pass filter can be used to filter the negative-sequence current injection weight and the zero-sequence voltage injection weight, specifically as follows:

[0094]

[0095]

[0096] in, This is the filter coefficient, usually taken as 0.2; To control the cycle.

[0097] The above-described scheme, by applying a first-order low-pass filter to the initial injection coefficients, effectively suppresses weight abrupt changes caused by instantaneous voltage and current fluctuations or noise, and avoids jumps in negative-sequence current or zero-sequence voltage commands. This makes the voltage equalization control process smoother, reduces stress impacts on the converter and modulation wave distortion, and improves the dynamic response quality and operational stability of the system.

[0098] In one embodiment, the method further includes: obtaining the sum of the first phase unbalanced power, the sum of the second phase unbalanced power, and the sum of the third phase unbalanced power based on the three-phase unbalanced power, and determining the maximum unbalanced power sum; if the maximum unbalanced power sum is greater than a preset power threshold, then step 204 is executed; if the maximum unbalanced power sum is less than or equal to the preset power threshold, then the zero-sequence voltage injection weight is configured to 0, and the negative-sequence current injection weight is configured to 1.

[0099] The sum of the unbalanced power of the first phase is the absolute value of the sum of all unbalanced power in phase A, which is also the first unbalanced power of the first three phases corresponding to phase A. The second and third phase unbalanced power corresponding to A The third three-phase unbalanced power corresponding to A That is, the total unbalanced power of the first phase is expressed as Similarly, the total unbalanced power of the second phase is expressed as... The sum of the unbalanced power of the third phase is expressed as The preset power threshold is used to determine whether the phase-to-phase voltage deviation is extremely small. Its magnitude is not unique. For example, in one embodiment, 0.02 pu (per unit value) can be selected.

[0100] In this embodiment, a dead-zone determination logic is introduced. First, the absolute values ​​of the total unbalanced power of phases A, B, and C are calculated based on the three-phase unbalanced power. Then, the maximum value is taken. If the sum of the maximum unbalanced power is less than or equal to a preset power threshold, it is considered to be in a dead zone. At this point, the phase-to-phase DC voltage deviation is already extremely small, and no complex coordinated control is required. To avoid unnecessary disturbances caused by frequent switching or simultaneous injection of the two strategies, the zero-sequence voltage injection weight is forcibly set to 0, and the negative-sequence current injection weight is set to 1, meaning that only the negative-sequence current strategy undertakes the minor adjustment task. If the sum of the maximum unbalanced power is greater than the preset power threshold, the negative-sequence current injection weight and the zero-sequence voltage injection weight are calculated and determined separately using the above calculation method.

[0101] The above scheme incorporates dead-zone judgment logic based on the sum of the maximum unbalanced power. When the three-phase voltage deviation is extremely small, zero-sequence voltage injection is forcibly shut down, and only the negative-sequence current handles the minor adjustments. This approach avoids frequent switching or meaningless competition between the two strategies under nearly balanced operating conditions, prevents controller output jitter, and reduces unnecessary injection losses.

[0102] Please see Figure 7 In one embodiment, step 108 includes steps 702 and 704.

[0103] Step 702: Limit the negative sequence current command and the zero sequence voltage command to obtain the target negative sequence current command and the target zero sequence voltage command.

[0104] Step 704: Generate a drive signal based on the target negative sequence current command and the target zero sequence voltage command.

[0105] Limiting refers to setting a maximum allowable amplitude for the command value based on the characteristics of the converter power devices, the modulation linearity region, and the system's safe operating boundaries, limiting any excess to the maximum value. The target negative sequence current command refers to the final d-axis and q-axis reference values ​​of the negative sequence current after limiting. The target zero sequence voltage command refers to the final d-axis and q-axis reference values ​​of the zero sequence voltage after limiting.

[0106] In this embodiment, after obtaining the negative-sequence current command and the zero-sequence voltage command, the maximum allowable absolute value of each command is set based on the current withstand capability of the power switching devices in the converter, the DC bus voltage limit, and the upper limit of the PWM modulation ratio (to avoid overmodulation), and then analyzed and processed. If the original command exceeds the limit, it is output at the maximum value; otherwise, it is output at the original value, thus obtaining the target negative-sequence current command and the target zero-sequence voltage command.

[0107] Subsequently, the negative-sequence current command is fed into the inner current loop for tracking and regulation, while the zero-sequence voltage command is superimposed onto the three-phase modulation wave. Finally, a drive signal is generated via PWM modulation to control the on / off state of the converter valve power switch. Thus, limiting ensures that under any operating condition, the commands issued by the controller will not exceed the hardware safety and modulation linearity range.

[0108] The above scheme, by limiting the negative-sequence current command and the zero-sequence voltage command before generating the drive signal, ensures that the final executed value always remains within the converter's hardware capabilities and modulation linearity range. This fundamentally prevents voltage equalization control failure or even equipment protection activation caused by over-modulation or overcurrent, ensuring the system's safe operating boundaries while achieving the voltage equalization target.

[0109] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages in other steps. It is understood that the steps in different embodiments can be freely combined as needed, and all non-contradictory solutions formed by such combinations are within the scope of protection of this application.

[0110] Based on the same inventive concept, this application also provides a converter phase-to-phase pressure equalization control device for implementing the converter phase-to-phase pressure equalization control method described above. The solution provided by this device is similar to the solution described in the above method; therefore, the specific limitations of one or more converter phase-to-phase pressure equalization control device embodiments provided below can be found in the limitations of the converter phase-to-phase pressure equalization control method described above, and will not be repeated here.

[0111] Please see Figure 8 This application provides a converter phase-to-phase voltage equalization control device, which includes a parameter acquisition module 802, a weight analysis module 804, an instruction generation module 806, and a drive control module 808.

[0112] The parameter acquisition module 802 is used to acquire the three-phase AC voltage and three-phase output current on the AC grid side of the converter, as well as the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter; the weight analysis module 804 is used to determine the negative sequence current injection weight, the zero sequence voltage injection weight, and the full negative sequence current injection amount required for a single negative sequence current injection strategy and the full zero sequence voltage injection amount required for a single zero sequence voltage injection strategy based on the three-phase AC voltage, three-phase DC voltage, and three-phase output current; the instruction generation module 806 is used to determine the negative sequence current instruction based on the negative sequence current injection weight and the full negative sequence current injection amount, and to determine the zero sequence voltage instruction based on the zero sequence voltage injection weight and the full zero sequence voltage injection amount; the drive control module 808 is used to generate drive signals based on the negative sequence current instruction and the zero sequence voltage instruction.

[0113] In one embodiment, the weight analysis module 804 is further configured to extract the positive-sequence voltage dq-axis component, negative-sequence voltage dq-axis component, positive-sequence current dq-axis component, and negative-sequence current dq-axis component based on the three-phase AC voltage and three-phase output current; perform imbalance analysis based on the three-phase DC voltage, positive-sequence voltage dq-axis component, negative-sequence voltage dq-axis component, positive-sequence current dq-axis component, and negative-sequence current dq-axis component to determine the three-phase unbalanced power; determine the full negative-sequence current injection amount required for a single negative-sequence current injection strategy and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy based on the three-phase unbalanced power, positive-sequence voltage dq-axis component, positive-sequence current dq-axis component, and negative-sequence current dq-axis component; and determine the negative-sequence current injection weight and the zero-sequence voltage injection weight based on the three-phase unbalanced power.

[0114] In one embodiment, the weighting analysis module 804 is further configured to determine the three-phase average value of the three-phase DC voltage; determine the first three-phase unbalanced power caused by the three-phase DC voltage deviation based on the three-phase DC voltage and the three-phase average value; determine the second three-phase unbalanced power caused by the interaction of negative-sequence voltage and positive-sequence current based on the dq-axis component of negative-sequence voltage and the dq-axis component of positive-sequence current; and determine the third three-phase unbalanced power caused by the interaction of positive-sequence voltage and negative-sequence current based on the dq-axis component of positive-sequence voltage and the dq-axis component of negative-sequence current.

[0115] In one embodiment, the weight analysis module 804 is further configured to determine the full negative sequence current injection amount required for a single negative sequence current injection strategy based on the first three-phase unbalanced power, the second three-phase unbalanced power, and the positive sequence voltage dq-axis component; and to determine the full zero sequence voltage injection amount required for a single zero sequence voltage injection strategy based on the first three-phase unbalanced power, the second three-phase unbalanced power, the third three-phase unbalanced power, and the positive sequence current dq-axis component and the negative sequence current dq-axis component.

[0116] In one embodiment, the weight analysis module 804 is further configured to perform positive and negative sequence separation based on the three-phase AC voltage and the three-phase output current, and determine the positive sequence voltage amplitude, negative sequence voltage amplitude, and positive sequence current amplitude; determine the negative sequence current strategy capability coefficient and the zero sequence voltage strategy capability coefficient based on the positive sequence voltage amplitude, negative sequence voltage amplitude, and positive sequence current amplitude; and determine the negative sequence current injection weight and the zero sequence voltage injection weight based on the negative sequence current strategy capability coefficient, the zero sequence voltage strategy capability coefficient, and the three-phase unbalanced power.

[0117] In one embodiment, the weight analysis module 804 is further configured to determine the initial negative sequence current injection weight and the initial zero sequence voltage injection weight based on the negative sequence current strategy capability coefficient, the zero sequence voltage strategy capability coefficient, and the three-phase unbalanced power; and to perform filtering processing based on the initial negative sequence current injection weight and the initial zero sequence voltage injection weight to obtain the negative sequence current injection weight and the zero sequence voltage injection weight.

[0118] In one embodiment, the weight analysis module 804 is further configured to obtain the sum of the first phase unbalanced power, the sum of the second phase unbalanced power, and the sum of the third phase unbalanced power based on the three-phase unbalanced power, and determine the maximum unbalanced power sum; if the maximum unbalanced power sum is greater than a preset power threshold, then the operation of determining the negative sequence current injection weight and the zero sequence voltage injection weight based on the three-phase unbalanced power is performed; if the maximum unbalanced power sum is less than or equal to the preset power threshold, then the zero sequence voltage injection weight is configured to 0, and the negative sequence current injection weight is configured to 1.

[0119] In one embodiment, the drive control module 808 is further configured to perform amplitude limiting processing on the negative sequence current command and the zero sequence voltage command to obtain the target negative sequence current command and the target zero sequence voltage command; and generate a drive signal based on the target negative sequence current command and the target zero sequence voltage command.

[0120] Each module in the aforementioned converter phase-to-phase voltage equalization control device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0121] This application provides a converter including a connected converter circuit and a controller, the controller being used to perform the steps of the above method.

[0122] The implementation method of phase-to-phase voltage equalization control of the converter is as shown in the above embodiments and accompanying drawings, and will not be repeated here. This converter has adaptive and coordinated adjustment capabilities. Regardless of whether the power grid is in a symmetrical, lightly loaded, heavily loaded, slightly unbalanced, or significantly asymmetrical voltage drop condition, the converter can automatically allocate the injection weights of negative sequence current and zero sequence voltage, always achieving phase-to-phase voltage equalization with minimal injection cost, significantly improving the converter's tolerance to harsh power grid conditions and operational reliability.

[0123] This application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the following steps:

[0124] The system acquires the three-phase AC voltage and three-phase output current on the AC grid side of the converter, as well as the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter. Based on the three-phase AC voltage, three-phase DC voltage, and three-phase output current, it determines the negative-sequence current injection weight, the zero-sequence voltage injection weight, the full negative-sequence current injection amount required for a single negative-sequence current injection strategy, and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy. Based on the negative-sequence current injection weight and the full negative-sequence current injection amount, it determines the negative-sequence current command, and based on the zero-sequence voltage injection weight and the full zero-sequence voltage injection amount, it determines the zero-sequence voltage command. Finally, it generates drive signals based on the negative-sequence current command and the zero-sequence voltage command.

[0125] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0126] The system acquires the three-phase AC voltage and three-phase output current on the AC grid side of the converter, as well as the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter. Based on the three-phase AC voltage, three-phase DC voltage, and three-phase output current, it determines the negative-sequence current injection weight, the zero-sequence voltage injection weight, the full negative-sequence current injection amount required for a single negative-sequence current injection strategy, and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy. Based on the negative-sequence current injection weight and the full negative-sequence current injection amount, it determines the negative-sequence current command, and based on the zero-sequence voltage injection weight and the full zero-sequence voltage injection amount, it determines the zero-sequence voltage command. Finally, it generates drive signals based on the negative-sequence current command and the zero-sequence voltage command.

[0127] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, performs the following steps:

[0128] The system acquires the three-phase AC voltage and three-phase output current on the AC grid side of the converter, as well as the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter. Based on the three-phase AC voltage, three-phase DC voltage, and three-phase output current, it determines the negative-sequence current injection weight, the zero-sequence voltage injection weight, the full negative-sequence current injection amount required for a single negative-sequence current injection strategy, and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy. Based on the negative-sequence current injection weight and the full negative-sequence current injection amount, it determines the negative-sequence current command, and based on the zero-sequence voltage injection weight and the full zero-sequence voltage injection amount, it determines the zero-sequence voltage command. Finally, it generates drive signals based on the negative-sequence current command and the zero-sequence voltage command.

[0129] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for controlling phase-to-phase voltage equalization in a converter, characterized in that, The method includes: The three-phase AC voltage and three-phase output current on the AC grid side of the converter, as well as the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter, are obtained. Based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current, determine the negative-sequence current injection weight, the zero-sequence voltage injection weight, and the full negative-sequence current injection amount required by a single negative-sequence current injection strategy and the full zero-sequence voltage injection amount required by a single zero-sequence voltage injection strategy; wherein, the sum of the negative-sequence current injection weight and the zero-sequence voltage injection weight is 1. The negative sequence current command is determined based on the negative sequence current injection weight and the full negative sequence current injection amount, and the zero sequence voltage command is determined based on the zero sequence voltage injection weight and the full zero sequence voltage injection amount. A drive signal is generated based on the negative sequence current command and the zero sequence voltage command; the drive signal is used to drive the converter circuit of the converter to operate.

2. The method according to claim 1, characterized in that, The step of determining the negative-sequence current injection weight, the zero-sequence voltage injection weight, and the full-scale negative-sequence current injection amount required for a single negative-sequence current injection strategy and the full-scale zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current includes: Based on the three-phase AC voltage and the three-phase output current, extract the positive sequence voltage dq-axis component, the negative sequence voltage dq-axis component, the positive sequence current dq-axis component, and the negative sequence current dq-axis component. An imbalance analysis is performed based on the three-phase DC voltage, the positive-sequence voltage dq-axis component, the negative-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component to determine the three-phase unbalanced power. Based on the three-phase unbalanced power, the positive-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component, determine the full amount of negative-sequence current injection required for a single negative-sequence current injection strategy, and the full amount of zero-sequence voltage injection required for a single zero-sequence voltage injection strategy. Based on the three-phase unbalanced power, the negative sequence current injection weight and the zero sequence voltage injection weight are determined.

3. The method according to claim 2, characterized in that, The step of performing unbalance analysis based on the three-phase DC voltage, the positive-sequence voltage dq-axis component, the negative-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component to determine the three-phase unbalanced power includes: Determine the three-phase average value of the three-phase DC voltage; Based on the three-phase DC voltage and the three-phase average value, determine the first three-phase unbalanced power caused by the three-phase DC voltage deviation; The second three-phase unbalanced power caused by the interaction of negative sequence voltage and positive sequence current is determined based on the negative sequence voltage dq axis component and the positive sequence current dq axis component. The third three-phase unbalanced power caused by the interaction of positive sequence voltage and negative sequence current is determined based on the positive sequence voltage dq axis component and the negative sequence current dq axis component.

4. The method according to claim 3, characterized in that, The step of determining the full negative-sequence current injection amount required for a single negative-sequence current injection strategy and the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy based on the three-phase unbalanced power, the positive-sequence voltage dq-axis component, the positive-sequence current dq-axis component, and the negative-sequence current dq-axis component includes: Based on the first three-phase unbalanced power, the second three-phase unbalanced power, and the dq-axis component of the positive-sequence voltage, determine the full amount of negative-sequence current injection required for a single negative-sequence current injection strategy. Based on the first three-phase unbalanced power, the second three-phase unbalanced power, the third three-phase unbalanced power, and the positive-sequence current dq-axis component and the negative-sequence current dq-axis component, determine the full zero-sequence voltage injection amount required for a single zero-sequence voltage injection strategy.

5. The method according to claim 2, characterized in that, The step of determining the negative sequence current injection weight and the zero sequence voltage injection weight based on the three-phase unbalanced power includes: Based on the three-phase AC voltage and the three-phase output current, the positive and negative sequences are separated to determine the positive sequence voltage amplitude, negative sequence voltage amplitude, and positive sequence current amplitude. Based on the positive-sequence voltage amplitude, the negative-sequence voltage amplitude, and the positive-sequence current amplitude, determine the negative-sequence current strategy capability coefficient and the zero-sequence voltage strategy capability coefficient; The negative sequence current injection weight and the zero sequence voltage injection weight are determined based on the negative sequence current strategy capability coefficient, the zero sequence voltage strategy capability coefficient, and the three-phase unbalanced power.

6. The method according to claim 5, characterized in that, The step of determining the negative-sequence current injection weight and the zero-sequence voltage injection weight based on the negative-sequence current strategy capability coefficient, the zero-sequence voltage strategy capability coefficient, and the three-phase unbalanced power includes: Based on the negative sequence current strategy capability coefficient, the zero sequence voltage strategy capability coefficient, and the three-phase unbalanced power, determine the initial negative sequence current injection weight and the initial zero sequence voltage injection weight. The initial negative sequence current injection weight and the initial zero sequence voltage injection weight are filtered to obtain the negative sequence current injection weight and the zero sequence voltage injection weight.

7. The method according to claim 2, characterized in that, The method further includes: Based on the three-phase unbalanced power, the sum of the first-phase unbalanced power, the sum of the second-phase unbalanced power, and the sum of the third-phase unbalanced power are obtained, and the maximum sum of unbalanced power is determined. If the sum of the maximum unbalanced power is greater than the preset power threshold, then the step of determining the negative sequence current injection weight and the zero sequence voltage injection weight based on the three-phase unbalanced power is executed. If the sum of the maximum unbalanced power is less than or equal to the preset power threshold, then the zero-sequence voltage injection weight is configured to 0, and the negative-sequence current injection weight is configured to 1.

8. The method according to any one of claims 1-7, characterized in that, The step of generating a drive signal based on the negative-sequence current command and the zero-sequence voltage command includes: The negative-sequence current command and the zero-sequence voltage command are subjected to amplitude limiting processing to obtain the target negative-sequence current command and the target zero-sequence voltage command; A drive signal is generated based on the target negative sequence current command and the target zero sequence voltage command.

9. A converter phase-to-phase voltage equalization control device, characterized in that, The device includes: The parameter acquisition module is used to acquire the three-phase AC voltage and three-phase output current on the AC grid side of the converter, as well as the three-phase DC voltage of the three-phase switched capacitor bridge module in the converter. The weighting analysis module is used to determine the negative sequence current injection weight, the zero sequence voltage injection weight, and the full negative sequence current injection amount required by a single negative sequence current injection strategy and the full zero sequence voltage injection amount required by a single zero sequence voltage injection strategy, based on the three-phase AC voltage, the three-phase DC voltage, and the three-phase output current; wherein, the sum of the negative sequence current injection weight and the zero sequence voltage injection weight is 1. The instruction generation module is used to determine a negative sequence current instruction based on the negative sequence current injection weight and the full negative sequence current injection amount, and to determine a zero sequence voltage instruction based on the zero sequence voltage injection weight and the full zero sequence voltage injection amount. The drive control module is used to generate a drive signal based on the negative sequence current command and the zero sequence voltage command; the drive signal is used to drive the converter circuit of the converter to operate.

10. A converter, characterized in that, It includes a connected commutation circuit and a controller, the controller being used to perform the steps of the method according to any one of claims 1-8.

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