A method and system for coordinated control of parallel PEBB wind power converters

Abstract

This invention discloses a coordinated control method and system for parallel PEBB wind power converters. The method acquires the total system power, output current, output inductance parameters, and module status information of each PEBB module. It determines the circulating current compensation amount based on the differences in output current and output inductance parameters of each PEBB module, and determines the health weight of each PEBB module based on the module status information to form a corresponding power reference and coordinate the power output of each PEBB module. When any PEBB module is in a health degradation state, its health weight is updated and the power reference of each PEBB module is re-determined to reduce the power burden of the degradation module. When any PEBB module fails, it is isolated from the parallel system, and the system power sharing relationship is re-determined based on the operating capacity of the remaining PEBB modules. This allows for coordination of circulating current and power distribution among modules when module parameters and operating states change.

Description

Technical Field

[0001] This invention relates to the field of wind power converter control technology, and more specifically, to a coordinated control method and system for parallel PEBB wind power converters. Background Technology

[0002] Wind power converter control technology is commonly used to regulate the power conversion and output of wind turbine units. In high-power wind power converters, multiple power electronic building block (PEBB) modules can be connected in parallel to share the system output power. Each PEBB module typically outputs power according to a set power distribution relationship, and current sharing or circulating current regulation is performed based on the output current relationship between the modules to maintain parallel operation.

[0003] The existing technology has the following shortcomings:

[0004] On the one hand, different PEBB modules may have differences in output inductance parameters due to differences in manufacturing parameters and long-term operation. If circulating current adjustment is based solely on the difference in real-time output current, it is difficult to fully reflect the impact of the difference in output inductance parameters on the parallel current relationship, thus making it difficult for the circulating current adjustment to always match the current parameter state of each module.

[0005] On the other hand, the health status of different PEBB modules may gradually diverge due to long-term thermal cycling, heat dissipation conditions, and changes in device operating status. If the total system power is still allocated in a fixed manner, PEBB modules with poor health may continue to bear power that is not commensurate with their current operating capacity. When PEBB modules further degrade or fail to exit the system, if the original power bearing is maintained or the original total system power is directly redistributed to the remaining PEBB modules, it may also lead to excessive operating stress on degraded modules or power bearing by the remaining modules exceeding their current capacity.

[0006] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a coordinated control method and system for parallel PEBB wind power converters to solve the problems mentioned in the background art. Summary of the Invention

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A coordinated control method for parallel PEBB wind power converters includes:

[0009] Obtain the total system power and the output current, output inductance parameters, and module status information of each PEBB module;

[0010] The corresponding circulating current observation is determined based on the output current of each PEBB module, and the corresponding circulating current compensation amount is determined based on the circulating current observation of each PEBB module and the deviation of the output inductance parameters between each PEBB module.

[0011] The health weight of each PEBB module is determined based on the module status information. The total power of the system is allocated according to the health weight of each PEBB module. The power reference of each PEBB module is determined to control the power output of each PEBB module. The output of each PEBB module is compensated according to the corresponding circulating current compensation.

[0012] When any PEBB module is determined to be in a health degradation state based on the module status information, the health weight of the PEBB module is updated based on the module status information, and the power reference of each PEBB module is re-determined based on the updated health weight of each PEBB module in order to reduce the power reference of the PEBB module.

[0013] When any PEBB module is confirmed to have failed based on the module status information, that PEBB module is designated as the target PEBB module. The target PEBB module is isolated from the parallel system. The PEBB modules that continue to participate in parallel operation after isolation are designated as the remaining PEBB modules. The corresponding power reference is re-determined based on the health weight of each remaining PEBB module.

[0014] In a preferred embodiment, the corresponding circulating current compensation amount is determined based on the circulating current observation and the output inductance parameter deviation between each PEBB module, and the output of each PEBB module is compensated according to the circulating current compensation amount, including:

[0015] The average output inductance parameter is determined based on the output inductance parameter of each PEBB module, and the corresponding circulating current feedback compensation component is determined by feedback adjustment based on the circulating current observation of each PEBB module.

[0016] Based on the deviation between the output inductance parameters of each PEBB module and the average output inductance parameters, as well as the output current change rate of the corresponding PEBB module, the corresponding parameter feedforward compensation component is determined.

[0017] The corresponding circulating current compensation amount is determined based on the circulating current feedback compensation component and the parameter feedforward compensation component, and the corresponding circulating current root mean square value is determined based on the circulating current observation of each PEBB module.

[0018] When the root mean square value of the circulating current of any PEBB module exceeds the first threshold, the dq voltage reference of the PEBB module is corrected according to the corresponding circulating current compensation amount.

[0019] When the root mean square value of the circulating current of the PEBB module recovers to below the exit threshold and remains below the threshold for a preset time, the corresponding circulating current compensation amount is gradually restored to zero in a ramp manner, wherein the exit threshold is lower than the first threshold.

[0020] In a preferred embodiment, the health weight of each PEBB module is determined based on module status information, including:

[0021] The health status of the corresponding PEBB module is determined by selecting one or more state variables from the following: maximum junction temperature, thermal margin, current sharing deviation of internal branches of the module, collector-emitter saturation conduction voltage drop Vce(sat) drift of the insulated gate bipolar transistor (IGBT), communication quality, and the root mean square value of the circulating current determined according to the corresponding circulating current observation.

[0022] Within a set time window, statistics are performed on the selected state variables, and consistency is judged when multiple state variables are selected.

[0023] Based on the statistical results and in conjunction with the consistency judgment results when selecting multiple state variables, the health weight of the corresponding PEBB module is updated through a hysteresis mechanism, so that the worse the health status of the corresponding PEBB module, the smaller the health weight.

[0024] In a preferred embodiment, the total system power is allocated according to health weights to determine the power reference for each PEBB module, including:

[0025] The power allocation ratio of the corresponding PEBB module is determined based on the ratio of the health weight of each PEBB module to the sum of the health weights of all PEBB modules participating in parallel operation.

[0026] The total power of the system is allocated according to the power allocation ratio to determine the power reference for the corresponding PEBB module.

[0027] In a preferred embodiment, determining that any PEBB module is in a healthy degradation state based on module status information, and adjusting the power of PEBB modules in the healthy degradation state that continue to participate in parallel operation, including:

[0028] When at least one module status information of any PEBB module reaches the corresponding warning condition, and the status information of the modules with corresponding protection conditions in the PEBB module does not reach the corresponding protection conditions, the PEBB module is determined to be in a health degradation state.

[0029] Reduce the health weight and allowable power limit of the PEBB module, and redetermine the power reference of each PEBB module based on the updated health weight of each PEBB module;

[0030] When the power reference of a PEBB module in a health degradation state is redefined to be higher than the corresponding allowable power limit, the power reference of the PEBB module is limited to the allowable power limit, and the power released due to the limitation is borne by other PEBB modules that participate in parallel operation and have the ability to bear the remaining power.

[0031] When the remaining power carrying capacity of other PEBB modules participating in parallel operation is insufficient to carry the power released due to the aforementioned restrictions, the system power target is reduced according to the power that each PEBB module participating in parallel operation can currently carry, and the power reference of each PEBB module is re-determined according to the reduced system power target.

[0032] A rate of change limit is imposed on the power reference of each redefined PEBB module.

[0033] In a preferred embodiment, confirming a fault in any PEBB module based on module status information includes:

[0034] A consistency judgment is performed on multiple module status information related to the fault to be confirmed, so as to determine whether the multiple module status information jointly indicate the fault status.

[0035] When the number of times the consistency judgment result meets the corresponding fault confirmation condition reaches a set number, the corresponding PEBB module is confirmed to have failed.

[0036] If, before reaching the set number of times, there is a judgment period in which the consistency judgment result does not meet the corresponding fault confirmation condition, continuous confirmation is performed again.

[0037] In a preferred embodiment, isolating the target PEBB module from the parallel system includes:

[0038] Reduce the power reference of the target PEBB module to zero or a preset safe power value, and then perform PWM blocking on the target PEBB module;

[0039] After PWM is blocked, the AC output current of the target PEBB module is detected. When the AC output current of the target PEBB module is lower than the set threshold, the AC side isolation device of the target PEBB module is disconnected first, and then the DC side isolation device of the target PEBB module is disconnected.

[0040] In a preferred embodiment, the corresponding power reference is re-determined based on the health weight of each remaining PEBB module, including:

[0041] The current available power of each remaining PEBB module is determined based on its rated capacity and current thermal margin, and the sum of the current available power of each remaining PEBB module is determined as the available power of the remaining parallel system.

[0042] When the available power is not lower than the total system power, the total system power is redistributed according to the health weight of each remaining PEBB module, and the power reference of each remaining PEBB module is determined.

[0043] When the available power is lower than the total system power, the derated system power target is determined based on the available power, the derated system power target is allocated according to the health weight of each remaining PEBB module, the power reference of each remaining PEBB module is determined, and the rate of change of the derated system power target is limited.

[0044] In a preferred embodiment, it further includes:

[0045] Perform a status self-check on the PEBB module to be restored after isolation, and reduce the voltage difference between the DC voltage of the PEBB module and the common DC bus voltage by pre-charging.

[0046] When the voltage difference between the PEBB module to be restored and the common DC bus meets the set conditions and the communication synchronization conditions, the PEBB module is connected to the common DC bus and carrier synchronization with other PEBB modules participating in parallel operation is completed.

[0047] After setting both the active power reference and reactive power reference of the PEBB module to zero and synchronizing the AC output of the PEBB module with the AC parallel node, connect the AC output of the PEBB module to the AC parallel node.

[0048] The power reference of the PEBB module is increased according to the constrained rate of change, while the power reference of other PEBB modules participating in parallel operation is correspondingly decreased.

[0049] A coordinated control system for parallel PEBB wind power converters is characterized by comprising multiple PEBB modules, a common DC bus, AC parallel nodes, a module status acquisition unit, a module local controller, a main power coordination controller, AC-side isolation devices, and DC-side isolation devices.

[0050] The DC end of each PEBB module is connected to the common DC bus, and the AC output end is connected to the AC parallel node through the corresponding output inductor. Each PEBB module is equipped with a corresponding AC side isolation device between itself and the AC parallel node, and each PEBB module is equipped with a corresponding DC side isolation device between itself and the common DC bus.

[0051] The module status acquisition unit is used to acquire the output current and module status information of each PEBB module, and send the acquired information to the main power coordination controller. The local controller of each module is connected to the main power coordination controller.

[0052] The main power coordinator is used to obtain the total power of the system and the output inductance parameters of each PEBB module. It determines the corresponding circulating current observation based on the output current of each PEBB module, and determines the corresponding circulating current compensation based on the circulating current observation of each PEBB module and the deviation of the output inductance parameters between each PEBB module.

[0053] The main power coordination controller is also used to determine the health weight of each PEBB module based on the module status information, allocate the total power of the system based on the health weight of each PEBB module, determine the power reference of each PEBB module, and coordinate the output of each PEBB module based on the power reference of each PEBB module and the corresponding circulating current compensation. The local controller of each module is used to execute the control commands issued by the main power coordination controller.

[0054] The main power coordinating controller is also used to update the health weight of any PEBB module according to the module status information when it is determined that any PEBB module is in a health degradation state, and to re-determine the power reference of each PEBB module according to the updated health weight of each PEBB module, so as to reduce the power reference of the PEBB module.

[0055] The main power coordination controller is also used to control the corresponding AC-side isolation device and DC-side isolation device to isolate the PEBB module from the parallel system when any PEBB module fails, and to re-determine the corresponding power reference according to the health weight of the PEBB module that continues to participate in parallel operation after isolation.

[0056] The effects and advantages of the coordinated control method and system for parallel PEBB wind power converters of this invention:

[0057] Compared with existing technologies, this invention coordinates circulating current by simultaneously combining the real-time output current relationship of each PEBB module and the differences in output inductance parameters. This allows the circulating current regulation to take into account both the current parallel current state and the impact of parameter differences between modules on the parallel current relationship. By dynamically adjusting the power load relationship of each PEBB module based on module status information, PEBB modules in poor health conditions can bear lower power, and controlled load reduction is implemented when a module enters a health degradation state to reduce the possibility of it continuously bearing high operating stress. When a PEBB module fails and exits the system, the system power and the power load relationship of each module are re-determined by combining the actual power load capacity of the remaining PEBB modules. This avoids directly maintaining the original total system power when the remaining system capacity is insufficient, thus enabling the parallel PEBB wind power converter to maintain a more reasonable power coordination relationship when module parameters and operating states change. Attached Figure Description

[0058] Figure 1This is a flowchart of the method of the present invention;

[0059] Figure 2 This is a schematic diagram of the structure of the present invention;

[0060] Figure 3 This is a flowchart illustrating the determination and deployment / release of the circulation compensation according to the present invention.

[0061] Figure 4 This is a flowchart of the health weight update and power allocation process of the present invention;

[0062] Figure 5 This is a flowchart of the PEBB module fault isolation and residual power reconfiguration process of the present invention;

[0063] Figure 6 This is a flowchart illustrating the PEBB module recovery and power recovery process of the present invention. Detailed Implementation

[0064] The technical solution of this application will be described below with reference to the accompanying drawings and specific embodiments. The embodiments are used to illustrate the method implementation process of this application and do not limit the scope of protection of this application.

[0065] This invention provides a coordinated control method and system for parallel PEBB wind power converters, applicable to operating scenarios where multiple PEBB modules are connected in parallel to jointly bear the system's output power. Due to factors such as differences in manufacturing parameters, long-term thermal cycling, changes in heat dissipation conditions, and changes in device operating status, differences in output inductance parameters and health status may gradually develop between different PEBB modules.

[0066] Given the aforementioned differences that vary during operation, relying solely on real-time output current differences among PEBB modules for circulating current adjustment is insufficient to fully reflect the impact of output inductance parameter differences on parallel current relationships. Allocating total system power in a fixed manner may also cause PEBB modules in poor health to continue bearing power incompatible with their current condition. Especially when a PEBB module has experienced health degradation but has not yet reached fault protection conditions, continuing to bear its original power load would increase its operational stress, while direct disconnection would fail to utilize its remaining controlled power regulation capabilities. Furthermore, if the original system power is still directly allocated to the remaining PEBB modules after the PEBB module further fails and exits the system, it may exceed the current actual power capacity of the remaining parallel system.

[0067] Therefore, the technical problem to be solved by the present invention is to coordinate the circulating current and power sharing relationship between multiple PEBB modules when they are operating in parallel and there are differences in output inductance parameters and health status, and to make the power sharing of each PEBB module adapt to its current operating capacity when the health of the PEBB module degrades or fails.

[0068] Reference Figure 1 This invention provides a coordinated control method for parallel PEBB wind power converters, applicable to wind power converters composed of multiple PEBB modules connected in parallel. This method acquires the total system power, as well as the output current, output inductance parameters, and module status information of each PEBB module. On the one hand, it coordinates the circulating current among the parallel PEBB modules; on the other hand, it adjusts the power-sharing relationship of each PEBB module according to its operating status, and further implements power adjustment and operating status switching when a PEBB module experiences health degradation or failure. The total system power represents the power target that currently needs to be shared by all PEBB modules participating in parallel operation, and can be determined by the upper-level power control command of the wind power converter.

[0069] Specifically, the corresponding circulating current observation is determined based on the output current of each PEBB module, and the corresponding circulating current compensation amount is determined in combination with the output inductance parameter deviation between each PEBB module to compensate the output of each PEBB module. At the same time, the health weight of each PEBB module is determined based on the module status information, and the total power of the system is allocated according to the health weight of each PEBB module to determine the power reference of each PEBB module, so that multiple PEBB modules can jointly complete the system power sharing and circulating current coordination during parallel operation.

[0070] During operation, when any PEBB module is determined to be in a state of health degradation based on module status information, the health weight of that PEBB module is updated, and the power reference of each PEBB module is redefined to reduce the power burden of the health-degraded PEBB module. When any PEBB module is confirmed to have failed, the corresponding PEBB module is isolated from the parallel system, and the power burden relationship is redefined based on the operating capacity and health status of the remaining PEBB modules that continue to participate in parallel operation after isolation. When the available power of the remaining parallel system is lower than the total system power, the system power target is reduced accordingly.

[0071] For PEBB modules that need to be put back into operation after isolation, after meeting the corresponding recovery conditions, they should be enabled to complete DC-side access, carrier synchronization and AC-side access in sequence, and their power reference should be gradually increased. At the same time, the power references of other PEBB modules participating in parallel operation should be adjusted accordingly, so that the PEBB modules after recovery and reconnection can re-establish a coordinated power sharing relationship.

[0072] The implementation process of the method and system of this application will be described below with reference to specific embodiments. Figure 2The following embodiments all use a wind power converter consisting of three 700kW-class PEBB modules connected in parallel as an example. The three PEBB modules are denoted as PEBB1, PEBB2, and PEBB3, respectively. Their DC terminals are connected to a common DC bus, and their AC output terminals are connected to the AC parallel node through their corresponding output inductors. Each PEBB module is equipped with a module status acquisition unit and a module local controller, and DC-side isolation devices and AC-side isolation devices are respectively installed between each PEBB module and the common DC bus and the AC parallel node. The main power coordination controller acquires the total system power and the output current, output inductor parameters, and module status information of each PEBB module, and communicates with the module local controller corresponding to each PEBB module to coordinate the power output of each PEBB module.

[0073] Example 1 uses the parallel operation of three PEBB modules, PEBB1, PEBB2, and PEBB3, as an example. Figure 3 The circulation coordination process between each PEBB module is explained.

[0074] like Figure 3 As shown, during the circulating current coordination process, the corresponding circulating current observation is determined based on the output current of each PEBB module. A circulating current feedback compensation component is formed based on this observation, and a parameter feedforward compensation component is formed based on the output inductance parameter deviation and the corresponding output current change rate. The circulating current compensation amount is then formed based on the circulating current feedback compensation component and the parameter feedforward compensation component. Simultaneously, the root mean square (RMS) value of the circulating current is determined based on the circulating current observation, and the circulating current compensation is activated and deactivated based on this RMS value. During the process where the three PEBB modules jointly bear the system's output power, the main power coordination controller continuously acquires the output current of each PEBB module and determines the corresponding circulating current observation based on the relationship between the output currents of each PEBB module.

[0075] Although the three PEBB modules use the same level of output inductor, their actual output inductance parameters may differ. The output inductance parameters of each PEBB module can be obtained by measuring or calibrating the corresponding output inductor during equipment commissioning. For example, the output inductance parameters of PEBB1, PEBB2, and PEBB3 are 0.95mH, 1.05mH, and 1.00mH, respectively. During system power adjustments or changes in output current, these differences in output inductance parameters may cause deviations in the actual output current of different PEBB modules.

[0076] Let M be the number of PEBB modules currently operating in parallel, and let the output current of the m-th PEBB module be... Then, the average output current of the PEBB modules currently operating in parallel can be determined first: ;in, This represents the average output current of the PEBB modules currently operating in parallel. Let be the output current of the k-th PEBB module participating in parallel operation, where k is the summation index. Then, determine the circulating current observation of the m-th PEBB module based on the difference between the corresponding PEBB module's output current and the average output current. ;in, Let's define the circulating current observations for the m-th PEBB module. For the three-phase output current, the corresponding circulating current observations can be determined in the abc coordinate system, or the output current can be transformed to the dq synchronous rotating coordinate system, and the circulating current observations corresponding to the d-axis and q-axis can be determined separately.

[0077] The main power coordination controller also determines the average output inductance parameter based on the output inductance parameters of each PEBB module currently operating in parallel. For example, the arithmetic mean of the output inductance parameters of each PEBB module can be taken as the average output inductance parameter, and the difference between the output inductance parameter of each PEBB module and the average output inductance parameter can be taken as the corresponding output inductance parameter deviation. Taking the above three PEBB modules as an example, their average output inductance parameter is 1.00mH, and the output inductance parameter of PEBB2 has a deviation of 0.05mH relative to the average output inductance parameter.

[0078] Taking PEBB2 as an example, when its output current deviates from the average output current of the three PEBB modules, the main power coordination controller forms a corresponding circulating current feedback compensation component based on the circulating current observation of PEBB2 through feedback adjustment. The circulating current feedback compensation component is a voltage compensation component, and its compensation effect is used to reduce the circulating current observation corresponding to PEBB2.

[0079] Simultaneously, the main power coordinator generates a parameter feedforward compensation component based on the output inductor parameter deviation of PEBB2 and the corresponding output current change rate. This parameter feedforward compensation component is a voltage compensation component. For example, the magnitude of the parameter feedforward compensation can be determined based on the product of the output inductor parameter deviation and the output current change rate to reflect the difference in inductor voltage drop caused by the output inductor parameter deviation under the current output current change state. The output current change rate can be determined based on the output current difference between adjacent sampling times and the corresponding sampling time interval.

[0080] The main power coordination controller generates the circulating current compensation amount corresponding to PEBB2 based on the circulating current feedback compensation component and the parameter feedforward compensation component. For example, the two can be added together to obtain the circulating current compensation amount, which is then used to correct the d-axis and / or q-axis voltage references of PEBB2. When the circulating current compensation amount is determined in the abc coordinate system, it can be transformed to the dq synchronous rotating coordinate system to correct the corresponding d-axis and / or q-axis voltage references. The corresponding circulating current compensation amounts for PEBB1 and PEBB3 can be determined in the same way.

[0081] During operation, the main power coordinating controller can also determine the root mean square (RMS) value of the circulating current for the corresponding PEBB module within a set time window based on multiple continuously acquired circulating current observations. When the RMS value of the circulating current for any PEBB module exceeds a first threshold, the corresponding circulating current compensation for that PEBB module is activated, and its d-axis and / or q-axis voltage reference is corrected using the corresponding circulating current compensation amount. The first threshold can be preset according to the allowable circulating current level of the parallel PEBB modules.

[0082] When the root mean square value of the circulating current of the corresponding PEBB module drops below the exit threshold and remains below it for a preset time, the main power coordination controller gradually reduces the corresponding circulating current compensation amount according to a set ramp until the circulating current compensation is released. The exit threshold is lower than a first threshold. The preset duration can, for example, consist of several consecutive control cycles, thereby creating a hysteresis relationship between the entry and exit of the circulating current compensation.

[0083] Example 2 is based on the parallel operation of the above three PEBB modules, referring to... Figure 4 When the operating status of one of the PEBB modules gradually changes, the power bearing relationship can be adjusted according to the module status information of each PEBB module. This embodiment takes PEBB2 as an example of the gradual deterioration of heat dissipation conditions.

[0084] like Figure 4As shown, the main power coordination controller determines the corresponding health status and health weight of each PEBB module based on the module status information of each PEBB module. It then allocates the total system power according to the health weight of each PEBB module and determines the initial power allocation value. Combined with the corresponding allowable power limit, it determines the final power reference for each PEBB module. When the remaining power carrying capacity of other PEBB modules participating in parallel operation is insufficient, the system power target is reduced accordingly. During parallel operation, the main power coordination controller periodically acquires the module status information of each PEBB module and selects one or more state variables from the following to determine the health status of the corresponding PEBB module: maximum junction temperature, thermal margin, current sharing deviation of internal branches of the module, collector-emitter saturation conduction voltage drop Vce(sat) drift of the insulated gate bipolar transistor (IGBT), communication quality, and the root mean square value of the circulating current determined by circulating current observations.

[0085] Among them, the maximum junction temperature can be obtained from the temperature acquisition results or junction temperature estimation results inside the PEBB module; the thermal margin can be determined from the difference between the current maximum junction temperature and the corresponding junction temperature protection limit; the current sharing deviation of the internal branch can be determined from the deviation of the current of each internal branch relative to the average current of the branch; the Vce(sat) drift can be determined from the change of the current Vce(sat) relative to the initial healthy operating state of the PEBB module or the normal reference value recorded during the debugging phase; the communication quality can be characterized by at least one of communication packet loss, communication delay or synchronization status; the root mean square value of the circulating current can be determined from the circulating current observations as described in Example 1.

[0086] For the selected state variables, the main power coordinator performs statistical analysis within a set time window. For example, it can generate corresponding statistical results based on the average value, maximum value, or trend over multiple consecutive sampling periods. When multiple state variables are selected simultaneously, consistency judgment can be performed on the statistical results. For example, if the maximum junction temperature of PEBB2 continuously increases while the thermal margin continuously decreases within the same statistical time window, and both state variables indicate that the thermal state of PEBB2 is changing in an unfavorable direction, then the corresponding statistical results can be determined to meet the consistency judgment. When more state variables are selected, the consistency judgment can also be determined to be valid when the number of state variables reflecting the deterioration of the health state reaches a set number.

[0087] In this embodiment, PEBB1 and PEBB3 maintain normal operation, while PEBB2 experiences a gradual deterioration in heat dissipation, causing its maximum junction temperature to rise continuously and its thermal margin to decrease accordingly. For example, the maximum junction temperature of PEBB2 reaches 95°C, which meets the warning condition corresponding to 90°C, but has not yet met the protection condition corresponding to 110°C. Furthermore, the status information of other modules in PEBB2 with corresponding protection conditions has not met their respective protection conditions. Therefore, PEBB2 is determined to be in a state of health degradation, and it is not immediately isolated from the parallel system.

[0088] The main power coordination controller can pre-set the correspondence between different module states and health weights. For example, the corresponding health weight can be determined based on the normal range, warning range, and corresponding trend of state variables such as maximum junction temperature and thermal margin. When multiple state variables are used, the health weight can be determined by combining the statistical results and consistency judgment results of each state variable.

[0089] In this embodiment, the module status information of PEBB1 and PEBB3 remains within the normal operating range, and their health weight remains at 1; the maximum junction temperature of PEBB2 enters the warning range, and the thermal margin continues to decrease, and the consistency judgment between the two is established. Therefore, according to the pre-set correspondence, the health weight of PEBB2 is adjusted from 1 to 0.7.

[0090] Health weights can be updated using a hysteresis mechanism. For example, when PEBB2 meets the conditions for reducing its health weight, its health weight is reduced, and only after the relevant state variables recover to the corresponding recovery range and remain continuously for a preset duration is its health weight increased, in order to reduce the frequent changes in health weights and power references caused by fluctuations in module state information within the critical range.

[0091] After determining the health weight of each PEBB module, the main power coordination controller determines the corresponding power allocation ratio based on the health weight of each PEBB module. The initial power allocation value of the m-th PEBB module according to its health weight can be determined, for example, by the following formula: ;in, This represents the initial power allocation value for the m-th PEBB module. The total power of the system. Let m be the health weight of the m-th PEBB module. Let M be the health weight of the k-th PEBB module participating in parallel operation, M be the number of PEBB modules currently participating in parallel operation, and k be the summation index.

[0092] For example, with a total system power of 1200kW, when PEBB1, PEBB2, and PEBB3 are all in normal condition and their health weights are all 1, each of the three PEBB modules will handle approximately 400kW. When the health weight of PEBB2 decreases to 0.7, the initial power allocation values ​​of the three PEBB modules are re-determined based on the updated health weights, resulting in a decrease in the power handling ratio of PEBB2 and a corresponding increase in the power handling ratios of PEBB1 and PEBB3.

[0093] For PEBB2 modules in a health degradation state, their allowable power limit is further reduced. In practice, allowable power limits corresponding to different health states can be preset, and this correspondence can be determined by combining the rated capacity, current thermal margin, and safe operation requirements of the PEBB module. For example, when the PEBB module is in normal operation, its allowable power limit can be set according to its corresponding rated capacity; when the PEBB module enters a health degradation state, the allowable power limit can be reduced accordingly based on its current thermal margin. In this embodiment, the allowable power limit corresponding to the current health state of PEBB2 is, for example, 300kW. Therefore, when the initial power allocation value of PEBB2 obtained based on the health weight is higher than 300kW, the final power reference of PEBB2 is limited to 300kW. When the initial power allocation value of the corresponding PEBB module is not higher than its allowable power limit, the corresponding power reference can be determined according to the initial power allocation value.

[0094] The power released by PEBB2 due to the aforementioned upper limit constraint is continued to be borne by PEBB1 and PEBB3, which have the capacity to bear the remaining power. In this embodiment, both PEBB1 and PEBB3 have sufficient capacity to bear the remaining power, and their health weights are the same. Therefore, the final power references for the three PEBB modules can be adjusted, for example, to 450kW, 300kW, and 450kW, so that the total system power is still maintained at 1200kW.

[0095] When other PEBB modules participating in parallel operation have sufficient remaining power capacity, the current system power target can be maintained in the manner described above. If the remaining power capacity of other PEBB modules participating in parallel operation is insufficient to handle all the power released by the healthy degraded PEBB modules, the system power target will be reduced accordingly based on the power currently handled by each participating PEBB module, and the power reference for each PEBB module will be redefined under the reduced system power target.

[0096] The aforementioned power adjustment employs a rate-of-change limitation, gradually reducing the power reference of PEBB2 to 300kW, and correspondingly gradually increasing the power references of PEBB1 and PEBB3, until a power sharing relationship of 450kW, 300kW, and 450kW is formed.

[0097] Example 3, based on the premise that PEBB2 is in a healthy degradation state and continues to participate in parallel operation as described in Example 2, refers to... Figure 5 Taking the further deterioration of PEBB2's operating state and the fulfillment of fault confirmation conditions as an example, this paper explains its fault confirmation, isolation, and power reconfiguration process after isolation. Figure 5 As shown, after the fault confirmation conditions are met continuously, the PEBB module is confirmed to have failed and is identified as the target PEBB module. Its power reference is reduced and PWM is locked. After the AC output current drops below the set threshold, the AC side isolation device and the DC side isolation device are disconnected in sequence. After isolation is completed, the available power of the remaining parallel system is determined according to the rated capacity of the remaining PEBB modules and the current thermal margin. Whether to reduce the system power target is determined according to whether the available power can cover the total power of the original system.

[0098] While PEBB2 continues to operate in a health degradation state, the main power coordination controller continuously acquires multiple module status information related to potential faults. In this embodiment, PEBB2 subsequently experiences output overcurrent, and simultaneously detects an abnormal change in the IGBT's Vce(sat) relative to the normal baseline value recorded during PEBB2's initial healthy operation or commissioning phase. These two module status information items are used as the basis for determining the corresponding fault to be confirmed.

[0099] When both output overcurrent and Vce(sat) anomalies simultaneously meet their respective fault confirmation conditions within the same judgment cycle, the consistency judgment for that judgment cycle is determined to meet the fault confirmation conditions. To prevent a single current fluctuation or instantaneous detection anomaly from directly causing PEBB2 to exit the parallel system, the consistency judgment result is continuously confirmed.

[0100] In this embodiment, when the above-mentioned fault confirmation conditions are met for three consecutive judgment cycles, a fault is confirmed in PEBB2, and PEBB2 is identified as the target PEBB module. If there are judgment cycles in which the fault confirmation conditions are not met before the continuous confirmation is completed, the continuous confirmation is performed again. The number of continuous confirmations can be preset according to the fault type and control response requirements.

[0101] After confirming that PEBB2 has failed, first reduce the power reference of PEBB2 so that its power load is gradually reduced to zero or a preset safe power value. Then, the local controller of PEBB2 module will perform PWM blocking.

[0102] After PWM is disabled, the AC output current of PEBB2 continues to be monitored. When the AC output current drops below a set threshold, the AC-side isolation device between PEBB2 and the AC parallel node is first disconnected, and then the DC-side isolation device between PEBB2 and the common DC bus is disconnected, causing PEBB2 to exit the parallel system. The set threshold can be set according to the allowable breaking current level of the AC-side isolation device and the safe exit requirements of the PEBB module.

[0103] After PEBB2 completes isolation, PEBB1 and PEBB3 continue to participate in parallel operation as the remaining PEBB modules. The main power coordination controller determines the power that PEBB1 and PEBB3 can continue to handle based on their rated capacity and current thermal margin, and determines the available power of the remaining parallel system accordingly.

[0104] In practical implementation, during the commissioning of PEBB modules, a correspondence between different thermal margin ranges and the currently allowed power of the PEBB modules can be pre-established based on the power that the PEBB modules can continuously bear under different thermal states. The currently allowed power does not exceed the rated capacity of the corresponding PEBB module. When the thermal margin of the remaining PEBB modules is within the normal operating range, their current available power can be close to their corresponding rated capacity; when the thermal margin decreases, their current available power is reduced accordingly based on the aforementioned correspondence. The available power of the remaining PEBB modules is then summed to obtain the available power of the remaining parallel system.

[0105] For example, if the total power of the system before PEBB2 isolation is 1200kW, and PEBB1 and PEBB3 are both 700kW-class PEBB modules with current thermal margins within their normal operating range capable of continuing to handle the corresponding power, then the available power of the remaining parallel system can cover the original system's total power of 1200kW. Therefore, the original total system power target is maintained, and the power references for PEBB1 and PEBB3 are redefined based on their health weights. When the health weights of PEBB1 and PEBB3 are the same, they can each handle approximately 600kW.

[0106] Under another operating condition, if PEBB2 is isolated, and based on the rated capacity and current thermal margin of PEBB1 and PEBB3, the current power that PEBB1 can handle is determined to be 550kW and the current power that PEBB3 can handle is determined to be 500kW, then the remaining usable power of the parallel system is 1050kW, which is lower than the total system power of 1200kW before the fault. In this case, 1050kW can be set as the derated system power target, and then the corresponding power reference can be re-determined based on the health weights of PEBB1 and PEBB3. For example, when the health weights of PEBB1 and PEBB3 are the same, they can each handle approximately 525kW.

[0107] When the system power changes from the pre-fault power level to the derated system power target, a rate of change limit is imposed on the derated system power target to gradually transition the system output power to the new power level.

[0108] Example 4, based on PEBB2 exiting the parallel system as described in Example 3, refers to... Figure 6 Taking PEBB2 as an example, after being repaired or replaced and put back into operation, the process of its reintegration is explained. Figure 6 As shown, the PEBB module to be restored and connected undergoes a status self-test. When all selected status self-test items are within the corresponding normal range or valid state, the status self-test is confirmed to be passed and pre-charging is performed, while the communication synchronization status is confirmed. After the DC voltage difference condition and communication synchronization condition are both met, the PEBB module is connected to the common DC bus and carrier synchronization with other PEBB modules participating in parallel operation is completed. Subsequently, the active power reference and reactive power reference of the PEBB module are both set to zero, and its AC output is kept synchronized with the AC parallel node. Then, its AC output terminal is connected to the AC parallel node. After the AC side connection is completed, the power reference of the PEBB module is gradually increased according to the constrained rate of change, while the power reference of other PEBB modules participating in power distribution is correspondingly decreased.

[0109] After PEBB2 is repaired or replaced, it enters a state awaiting restoration and integration. First, a status self-test is performed. This self-test may include one or more checks on module identity, output inductor parameters, temperature detection, drive feedback, insulation status, and the communication link. When all selected self-test items are within their corresponding normal ranges or valid states, the PEBB2 self-test is considered passed, and PEBB2 is pre-charged to gradually bring its DC voltage close to the common DC bus voltage.

[0110] For example, the current common DC bus voltage is 1100V, and the DC voltage of PEBB2 after pre-charging reaches 1085V. In this embodiment, the allowable DC voltage difference connected to the common DC bus is set to, for example, 20V. The actual voltage difference between PEBB2 and the common DC bus is 15V, thus satisfying the DC voltage difference condition.

[0111] Simultaneously, the communication synchronization status of PEBB2 is confirmed. When PEBB2 can normally receive synchronization information sent by the main power coordinator and maintain a valid communication synchronization status, the communication synchronization condition is deemed met. If the DC voltage difference condition or the communication synchronization condition is not yet met, pre-charging continues and the communication synchronization status is confirmed until both the DC voltage difference condition and the communication synchronization condition are met. Once both the DC voltage difference condition and the communication synchronization condition are met, PEBB2 is connected to the common DC bus, and carrier synchronization between PEBB2 and other PEBB modules participating in parallel operation is completed according to the carrier synchronization reference of the parallel system.

[0112] After completing DC-side access and carrier synchronization, set both the active power reference and reactive power reference of PEBB2 to zero, and keep the AC output of PEBB2 synchronized with the AC parallel node. After meeting the above conditions, connect the AC output terminal of PEBB2 to the AC parallel node, so that PEBB2 first restores its electrical connection with the parallel system, and temporarily does not bear the system output power.

[0113] After the AC side connection is completed, the main power coordinating controller gradually increases the power reference of PEBB2 according to the constrained rate of change, while correspondingly decreasing the power reference of other PEBB modules participating in parallel operation.

[0114] For example, before PEBB2 is reintegrated, the total system power is 1200kW, with PEBB1 and PEBB3 each contributing approximately 600kW, and PEBB2's power reference being zero. During power restoration, for each increase in PEBB2's power reference, the main power coordination controller correspondingly reduces the total power reference of PEBB1 and PEBB3; when PEBB1 and PEBB3 have the same health weight, they can share the power reduction. As PEBB2 gradually restores its power contribution, the power references of PEBB1, PEBB2, and PEBB3 can be gradually adjusted from approximately 600kW, 0kW, and 600kW to approximately 400kW, 400kW, and 400kW, respectively. This allows PEBB1, PEBB2, and PEBB3 to re-establish a coordinated power contribution relationship after PEBB2's reintegration.

[0115] Example 5 is based on the above-described coordinated control method, with reference to... Figure 2 The coordinated control system for parallel PEBB wind power converters used to implement the aforementioned coordinated control method is further described below. The coordinated control system includes multiple PEBB modules, a common DC bus, AC parallel nodes, a module status acquisition unit, a module local controller, a main power coordinated controller, AC-side isolation devices, and DC-side isolation devices.

[0116] Each PEBB module's DC terminal is connected to a common DC bus, and its AC output terminals are connected to an AC parallel node via corresponding output inductors. Each PEBB module is connected to the AC parallel node via an AC-side isolation device, and each PEBB module is connected to the common DC bus via a corresponding DC-side isolation device.

[0117] The module status acquisition unit is used to acquire the output current and module status information of the corresponding PEBB module and send the acquired information to the main power coordination controller; the module local controller is connected to the main power coordination controller and is used to receive and execute the power reference and corresponding control commands issued by the main power coordination controller.

[0118] The main power coordination controller can receive power control commands from the upper level and determine the total system power based on these commands. The main power coordination controller is also used to acquire the output current, output inductance parameters, and module status information of each PEBB module; determine the corresponding circulating current observation based on the output current of each PEBB module; and determine the corresponding circulating current compensation amount based on the deviation between the circulating current observation and the output inductance parameters of each PEBB module. Furthermore, it is used to determine the health weight of each PEBB module based on the module status information, allocate the total system power according to the health weight of each PEBB module, determine the power reference for each PEBB module, and coordinate the output of each PEBB module based on the power reference and the corresponding circulating current compensation amount.

[0119] When any PEBB module meets the fault confirmation conditions, the main power coordination controller identifies that PEBB module as the target PEBB module and reduces its power reference, performs PWM blocking, and sequentially isolates the AC and DC sides in accordance with the method described in the previous embodiment. After isolation is completed, the corresponding power reference is re-determined based on the rated capacity, thermal margin, and health weight of the remaining PEBB modules.

[0120] For PEBB modules that need to be restored to parallel operation, the status self-test, pre-charging, DC-side access, carrier synchronization, AC-side access, and subsequent power restoration can be completed in accordance with the methods described in the aforementioned embodiments. The determination of circulating current observations and compensation amounts, the determination of health status and health weights, power allocation, fault confirmation and isolation, power reconfiguration after isolation, and the specific implementation methods for restoration to parallel operation can be performed in accordance with the methods described in the aforementioned embodiments.

[0121] The aforementioned coordinated control method and system for parallel PEBB wind power converters can be implemented through software, hardware, firmware, or a combination thereof.

[0122] The above embodiments are only used to illustrate the technical solutions of this application. Those skilled in the art can make adaptive settings for relevant parameters and control methods according to the number of PEBB modules, rated capacity and actual operating conditions.

Claims

1. A coordinated control method for parallel PEBB wind power converters, characterized in that, include: Obtain the total system power and the output current, output inductance parameters, and module status information of each PEBB module; The corresponding circulating current observation is determined based on the output current of each PEBB module, and the corresponding circulating current compensation amount is determined based on the circulating current observation of each PEBB module and the deviation of the output inductance parameters between each PEBB module. The health weight of each PEBB module is determined based on the module status information. The total power of the system is allocated according to the health weight of each PEBB module. The power reference of each PEBB module is determined to control the power output of each PEBB module. The output of each PEBB module is compensated according to the corresponding circulating current compensation. When any PEBB module is determined to be in a health degradation state based on the module status information, the health weight of the PEBB module is updated based on the module status information, and the power reference of each PEBB module is re-determined based on the updated health weight of each PEBB module in order to reduce the power reference of the PEBB module. When any PEBB module is confirmed to have failed based on the module status information, that PEBB module is designated as the target PEBB module. The target PEBB module is isolated from the parallel system. The PEBB modules that continue to participate in parallel operation after isolation are designated as the remaining PEBB modules. The corresponding power reference is re-determined based on the health weight of each remaining PEBB module.

2. The coordinated control method for parallel PEBB wind power converters according to claim 1, characterized in that, The corresponding circulating current compensation amount is determined based on the circulating current observations and the output inductance parameter deviations between each PEBB module. The output of each PEBB module is then compensated based on the circulating current compensation amount, including: The average output inductance parameter is determined based on the output inductance parameter of each PEBB module, and the corresponding circulating current feedback compensation component is determined by feedback adjustment based on the circulating current observation of each PEBB module. Based on the deviation between the output inductance parameters of each PEBB module and the average output inductance parameters, as well as the output current change rate of the corresponding PEBB module, the corresponding parameter feedforward compensation component is determined. The corresponding circulating current compensation amount is determined based on the circulating current feedback compensation component and the parameter feedforward compensation component, and the corresponding circulating current root mean square value is determined based on the circulating current observation of each PEBB module. When the root mean square value of the circulating current of any PEBB module exceeds the first threshold, the dq voltage reference of the PEBB module is corrected according to the corresponding circulating current compensation amount. When the root mean square value of the circulating current of the PEBB module recovers to below the exit threshold and remains below the threshold for a preset time, the corresponding circulating current compensation amount is gradually restored to zero in a ramp manner, wherein the exit threshold is lower than the first threshold.

3. The coordinated control method for parallel PEBB wind power converters according to claim 1, characterized in that, The health weight of each PEBB module is determined based on the module status information, including: The health status of the corresponding PEBB module is determined by selecting one or more state variables from the following: maximum junction temperature, thermal margin, current sharing deviation of internal branches of the module, collector-emitter saturation conduction voltage drop Vce(sat) drift of the insulated gate bipolar transistor (IGBT), communication quality, and the root mean square value of the circulating current determined according to the corresponding circulating current observation. Within a set time window, statistics are performed on the selected state variables, and consistency is judged when multiple state variables are selected. Based on the statistical results and in conjunction with the consistency judgment results when selecting multiple state variables, the health weight of the corresponding PEBB module is updated through a hysteresis mechanism, so that the worse the health status of the corresponding PEBB module, the smaller the health weight.

4. The coordinated control method for parallel PEBB wind power converters according to claim 1, characterized in that, The total system power is allocated based on health weights, and the power reference for each PEBB module is determined, including: The power allocation ratio of the corresponding PEBB module is determined based on the ratio of the health weight of each PEBB module to the sum of the health weights of all PEBB modules participating in parallel operation. The total power of the system is allocated according to the power allocation ratio to determine the power reference for the corresponding PEBB module.

5. The coordinated control method for parallel PEBB wind power converters according to claim 1, characterized in that, Based on module status information, any PEBB module is determined to be in a healthy degradation state. Power adjustments are then performed on PEBB modules in this healthy degradation state that continue to participate in parallel operation, including: When at least one module status information of any PEBB module reaches the corresponding warning condition, and the status information of the modules with corresponding protection conditions in the PEBB module does not reach the corresponding protection conditions, the PEBB module is determined to be in a health degradation state. Reduce the health weight and allowable power limit of the PEBB module, and redetermine the power reference of each PEBB module based on the updated health weight of each PEBB module; When the power reference of a PEBB module in a health degradation state is redefined to be higher than the corresponding allowable power limit, the power reference of the PEBB module is limited to the allowable power limit, and the power released due to the limitation is borne by other PEBB modules that participate in parallel operation and have the ability to bear the remaining power. When the remaining power carrying capacity of other PEBB modules participating in parallel operation is insufficient to carry the power released due to the aforementioned restrictions, the system power target is reduced according to the power that each PEBB module participating in parallel operation can currently carry, and the power reference of each PEBB module is re-determined according to the reduced system power target. A rate of change limit is imposed on the power reference of each redefined PEBB module.

6. The coordinated control method for parallel PEBB wind power converters according to claim 1, characterized in that, Based on the module status information, it can be confirmed that any PEBB module has failed, including: A consistency judgment is performed on multiple module status information related to the fault to be confirmed, so as to determine whether the multiple module status information jointly indicate the fault status. When the number of times the consistency judgment result meets the corresponding fault confirmation condition reaches a set number, the corresponding PEBB module is confirmed to have failed. If, before reaching the set number of times, there is a judgment period in which the consistency judgment result does not meet the corresponding fault confirmation condition, continuous confirmation is performed again.

7. The coordinated control method for parallel PEBB wind power converters according to claim 6, characterized in that, Isolate the target PEBB module from the parallel system, including: Reduce the power reference of the target PEBB module to zero or a preset safe power value, and then perform PWM blocking on the target PEBB module; After PWM is blocked, the AC output current of the target PEBB module is detected. When the AC output current of the target PEBB module is lower than the set threshold, the AC side isolation device of the target PEBB module is disconnected first, and then the DC side isolation device of the target PEBB module is disconnected.

8. The coordinated control method for parallel PEBB wind power converters according to claim 7, characterized in that, The corresponding power reference is re-determined based on the health weight of each remaining PEBB module, including: The current available power of each remaining PEBB module is determined based on its rated capacity and current thermal margin, and the sum of the current available power of each remaining PEBB module is determined as the available power of the remaining parallel system. When the available power is not lower than the total system power, the total system power is redistributed according to the health weight of each remaining PEBB module, and the power reference of each remaining PEBB module is determined. When the available power is lower than the total system power, the derated system power target is determined based on the available power, the derated system power target is allocated according to the health weight of each remaining PEBB module, the power reference of each remaining PEBB module is determined, and the rate of change of the derated system power target is limited.

9. The coordinated control method for parallel PEBB wind power converters according to claim 1, characterized in that, Also includes: Perform a status self-check on the PEBB module to be restored after isolation, and reduce the voltage difference between the DC voltage of the PEBB module and the common DC bus voltage by pre-charging. When the voltage difference between the PEBB module to be restored and the common DC bus meets the set conditions and the communication synchronization conditions, the PEBB module is connected to the common DC bus and carrier synchronization with other PEBB modules participating in parallel operation is completed. After setting both the active power reference and reactive power reference of the PEBB module to zero and synchronizing the AC output of the PEBB module with the AC parallel node, connect the AC output of the PEBB module to the AC parallel node. The power reference of the PEBB module is increased according to the constrained rate of change, while the power reference of other PEBB modules participating in parallel operation is correspondingly decreased.

10. A coordinated control system for parallel PEBB wind power converters, characterized in that, It includes multiple PEBB modules, a common DC bus, AC parallel nodes, a module status acquisition unit, a module local controller, a main power coordination controller, AC-side isolation devices, and DC-side isolation devices; The DC end of each PEBB module is connected to the common DC bus, and the AC output end is connected to the AC parallel node through the corresponding output inductor. Each PEBB module is equipped with a corresponding AC side isolation device between itself and the AC parallel node, and each PEBB module is equipped with a corresponding DC side isolation device between itself and the common DC bus. The module status acquisition unit is used to acquire the output current and module status information of each PEBB module, and send the acquired information to the main power coordination controller. The local controller of each module is connected to the main power coordination controller. The main power coordinator is used to obtain the total power of the system and the output inductance parameters of each PEBB module. It determines the corresponding circulating current observation based on the output current of each PEBB module, and determines the corresponding circulating current compensation based on the circulating current observation of each PEBB module and the deviation of the output inductance parameters between each PEBB module. The main power coordination controller is also used to determine the health weight of each PEBB module based on the module status information, allocate the total power of the system based on the health weight of each PEBB module, determine the power reference of each PEBB module, and coordinate the output of each PEBB module based on the power reference of each PEBB module and the corresponding circulating current compensation. The local controller of each module is used to execute the control commands issued by the main power coordination controller. The main power coordinating controller is also used to update the health weight of any PEBB module according to the module status information when it is determined that any PEBB module is in a health degradation state, and to re-determine the power reference of each PEBB module according to the updated health weight of each PEBB module, so as to reduce the power reference of the PEBB module. The main power coordination controller is also used to control the corresponding AC-side isolation device and DC-side isolation device to isolate the PEBB module from the parallel system when any PEBB module fails, and to re-determine the corresponding power reference according to the health weight of the PEBB module that continues to participate in parallel operation after isolation.

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