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　　3BHE039724R0C3D Alternative Names:

　　AC800PEC System Controller 3BHE039724R0C3D

　　3BHE039724R0C3D Controller Drive Module

　　High-Performance Excitation Control Unit 3BHE039724R0C3D

　　The ABB 3BHE039724R0C3D excitation controller is a core excitation control unit based on ABB’s high-performance AC 800PEC control platform. It belongs to the control-layer hardware of the ABB UNITROL excitation system series. It primarily handles the computation, control, and protection functions for synchronous motor excitation regulation, offering a control accuracy of ±0.5% and high-speed dynamic response capabilities.

　　Operating Principle

　　This excitation controller operates based on a closed-loop negative feedback control principle; the complete regulation process is as follows:

　　Signal Acquisition and Deviation Calculation: Real-time operating parameters—such as terminal voltage, stator current, and rotor excitation current of the synchronous generator or motor—are acquired via front-end measurement circuits. After converting these physical quantities into standard control signals, they are compared against internally preset reference values (such as voltage setpoints and excitation current setpoints) to generate a deviation signal. Control Algorithm Processing: It features a built-in, configurable PID control algorithm supporting multiple modes, such as Automatic Voltage Regulation (AVR) and Manual Field Current Regulation (FCR). Based on the magnitude and trend of error signals—and incorporating auxiliary logic like Power System Stabilizers (PSS), under/over-excitation limiters, and Volts-per-Hertz limiters—it calculates the trigger control values for the power rectification unit.

　　Excitation Power Output Control: The output trigger signals control the firing angle of the downstream thyristor rectifier bridge (or IGCT power unit) to adjust the magnitude of the rectified DC excitation current. Changes in excitation current synchronously alter the magnetic field strength of the synchronous motor rotor, thereby regulating the stator-side induced voltage and reactive power output.

　　Closed-Loop Feedback Correction: Adjusted operating parameters are recaptured by the acquisition circuit to continuously correct control errors, establishing a complete closed-loop control system that stabilizes the controlled variable within the set range.

　　Additionally, the controller integrates IGCT drive and snubber technologies, offering low conduction losses and high blocking voltage capabilities. It achieves a rapid response time of less than 20ms, meeting the need for quick regulation during grid transient conditions.

　　Core Functions

　　Terminal Voltage Stabilization Control: This is the fundamental core function of the excitation controller. Regardless of synchronous motor load fluctuations or grid voltage disturbances, it maintains the terminal voltage precisely at the set value by adjusting the excitation current in real-time, ensuring the quality of the supply voltage.

　　Reactive Power and Power Factor Regulation: During grid-connected operation, the unit's reactive power output is controlled by adjusting the excitation current, enabling rational reactive power distribution among parallel-connected units. It can also operate according to a set power factor to optimize the unit's power quality and operational efficiency.

　　Power System Stability Enhancement: It supports Power System Stabilizer (PSS) functionality to suppress low-frequency oscillations and improve the grid's transient stability. In the event of a grid fault, it can provide rapid voltage support through forced excitation, helping the system restore stable operation.Equipment Protection and Fault Handling: Integrates multiple protection logics—including monitoring for overcurrent, short-circuit, overvoltage, undervoltage, loss of excitation, and rotating diode faults. Under abnormal conditions, it rapidly executes limiting adjustments or triggers field-suppression sequences to prevent damage to the synchronous motor rotor and excitation power unit, thereby ensuring equipment safety.

　　Multi-mode Operation: Supports various operating modes such as automatic, manual, and preset control. Seamless, bumpless switching between modes is achievable, meeting operational requirements for unit startup, grid connection, load operation, and maintenance.

　　Application Areas

　　Power Generation Industry: Serves as the core control component for excitation systems in various synchronous generators. It is widely used in thermal, hydroelectric, gas turbine, combined-cycle, and pumped-storage power plants, accommodating generator units of diverse capacity ratings.

　　Large-scale Industrial Synchronous Drives: Used for the excitation control of large synchronous motors in sectors such as metallurgy, mining, chemicals, and building materials. It ensures smooth motor startup, variable-speed operation, and power factor optimization, making it suitable for high-power drive applications.

　　Power Grid Support Facilities: Supports synchronous condensers and dynamic reactive power compensation devices within substations. Through excitation regulation, it contributes to grid voltage support and reactive power adjustment, enhancing overall grid operational stability.

　　Industrial Automation Power Electronics Systems: Integrated into high-precision industrial power electronics control systems as an excitation control unit, providing reliable excitation regulation capabilities for power supply and drive equipment in industrial process control. ABB AC800PEC Series Excitation Control Module: Closed-Loop Feedback Control Architecture

　　The ABB AC800PEC serves as the core control platform for the UNITROL series excitation systems. Its closed-loop feedback control employs a layered, nested architecture—comprising "hardware-layered physical links," "dual-loop nested control logic," and "three-level real-time software scheduling"—capable of spanning the entire time scale from nanosecond-level pulse response to millisecond-level system regulation. It also supports dual-channel redundancy and fault tolerance, representing a classic architecture for high-performance synchronous motor excitation control.

　　I. Hardware Closed-Loop Physical Layer Architecture

　　In terms of the physical signal link, the complete closed-loop control system is divided into four functional layers, forming a continuous signal flow along the path of "acquisition → computation → output → feedback":

　　Front-end Signal Acquisition and Conditioning Layer: Centered on I/O modules such as the PEC80-CIO-FU (e.g., PC D235 A), this layer acts as the entry point for closed-loop signals. It is responsible for acquiring analog signals—such as synchronous motor terminal voltage, stator current, rotor excitation current, and winding temperature—as well as digital status signals from circuit breakers and limit switches. Equipped with built-in electrical isolation, filtering circuits, and high-precision A/D converters, it converts high-voltage field signals into standard digital signals suitable for controller processing; the typical analog sampling period is 400 μs. This layer also acquires feedback signals from the power stage, serving as the hardware medium for closed-loop feedback.

　　Core Control and Computation Layer: Centered on main CPU modules such as the 3BHE039724R0C3D and 3BHE046836R0101 GFD563A101 or 3BHE046836R0102 GFD563A102, this layer acts as the computational hub for closed-loop regulation. It receives digital signals from the acquisition layer and executes closed-loop regulation algorithms, limiting logic, and state machine operations to generate control commands. It supports dual-module hot-standby redundancy, where primary and backup units perform synchronous acquisition and computation; in the event of a fault, a bumpless transfer ensures the closed-loop control remains uninterrupted.

　　Pulse Output and Power Drive Layer: Implemented via FPGA hardware logic, this constitutes the ultra-high-speed execution layer. This layer receives firing angle commands from the control computation layer and generates high-precision, highly synchronized firing pulses for thyristors or IGCTs to directly drive the downstream power rectifier bridge. With a response speed in the 25-nanosecond range and no software computation latency, this layer ensures rapid and accurate excitation power output.

　　The feedback acquisition link consists of two stages: first, primary feedback, where core controlled variables—such as excitation current and generator terminal voltage—are transmitted from power-side sensors back to the front-end acquisition layer to form the main closed-loop control; second, pulse-level feedback, where the output and conduction states of the firing pulses are fed directly back to the FPGA layer, enabling microsecond-level pulse verification and rapid fault blocking to form a hardware-based micro-closed-loop.

　　II. Core Control Loop: Nested Dual-Loop Logic

　　The core functions of excitation control are implemented via a nested dual-loop structure comprising an outer voltage loop and an inner current loop. These two loops are decoupled based on time scales and work collaboratively to perform regulation tasks:

　　Outer Loop: Automatic Voltage Regulation (AVR, automatic mode)

　　Controlled Object: Terminal voltage of the synchronous generator or motor

　　Setpoint Input: System-preset voltage reference value; allows for the superposition of reactive power droop, PSS (Power System Stabilizer) auxiliary control, and remote voltage regulation commands

　　Feedback Input: RMS values of the three-phase terminal voltage transmitted from the acquisition layer

　　Regulation Algorithm: PID algorithm with filtering; control cycle ranges from 1 ms to several milliseconds

　　Function: As the outer loop, it maintains terminal voltage stability and responds to slow disturbances such as grid voltage fluctuations and load changes; its output serves as the setpoint for the inner current loop. Inner Loop: Excitation Current Regulation Loop (FCR, manual mode)

　　Controlled Variable: DC excitation current in the rotor circuit

　　Setpoint Input: Output command from the AVR outer loop (automatic mode) or manually set current reference value (manual mode)

　　Feedback Input: Sampled current value from the DC side of the excitation system

　　Regulation Algorithm: PI regulation algorithm; control cycle of 100–400 μs

　　Function: As the inner loop, it features a response speed significantly faster than the outer loop. It is responsible for rapidly tracking the current setpoint and suppressing fast disturbances—such as fluctuations in the excitation power supply or changes in rectifier bridge characteristics—serving as the direct control loop for excitation power output.

　　In addition to the two main loops, the architecture incorporates multiple closed-loop protection and limiting functions, including over-excitation limiting, under-excitation limiting, V/Hz limiting, and stator over-current limiting. When operating parameters approach safety thresholds, the limiters automatically take over the control loop to constrain the controlled variables within permissible ranges, thereby achieving an integrated closed-loop system for both protection and regulation.

　　III. Software Scheduling: Three-Level Real-Time Hierarchical Architecture

　　The AC800PEC platform categorizes various closed-loop control tasks into three software levels based on real-time requirements. Each level utilizes specific development tools and execution cycles, striking a balance between performance and flexibility:

　　Level 3: Ultra-high-speed hardware logic layer (nanosecond to microsecond range)

　　Implementation: FPGA-based, developed using VHDL; implemented as fixed firmware that cannot be modified by the user

　　Typical Cycle: 25 ns – 25 μs

　　Closed-loop Functions: Trigger pulse generation and modulation, pulse loss detection, hardware-level rapid blocking for over-current and over-voltage conditions, and high-speed I/O read/write operations. This layer constitutes a hardware-level micro-closed-loop, enabling the fastest fault response and precise pulse control. Level 2: Fast Control Algorithm Layer (Microsecond to Millisecond Range)

　　Implementation: Based on MATLAB/Simulink modeling; C code is automatically generated, downloaded, and executed.

　　Typical Cycle Time: 100 μs to 5 ms (the typical cycle for the main excitation loop is 400 μs).

　　Closed-loop Functions: Executes core AVR and FCR dual-loop regulation algorithms, PSS stability control, various limiter logic functions, and fault detection and handling. This is the core software layer for closed-loop excitation control, determining the system's regulation precision and dynamic response speed.

　　Level 1: System Monitoring and Management Layer (Millisecond Range and Above)

　　Implementation: Based on the IEC 61131-3 standard; programmed using the Control Builder tool.

　　Typical Cycle Time: 10 ms and above.

　　Closed-loop Functions: Handles control mode switching, setpoint distribution, parameter tuning, HMI interaction, communication with DCS/upper-level systems, event logging, and fault recording. While this layer does not directly participate in real-time regulation, it serves as the top-level management unit for the closed-loop system, facilitating control objective adjustments and system status monitoring.

　　IV. Redundant and Fault-Tolerant Closed-Loop Design

　　To ensure high reliability in industrial applications, the AC800PEC series closed-loop architecture supports a comprehensive redundancy design:

　　Dual-Channel Redundant Closed-Loop: Supports primary and backup control channels. Both channels independently acquire feedback signals and execute closed-loop algorithms synchronously, with outputs selected via a voting circuit. In the event of a single-channel failure, bumpless transfer occurs within ≤200 ms, ensuring the closed-loop regulation process remains uninterrupted.

　　Independent Feedback for Backup Channel: The backup channel continuously participates in signal acquisition and closed-loop calculations, maintaining a control output state synchronized with the primary channel. This ensures no control jumps occur during switching, thereby guaranteeing stable unit operation. 5. Complete Closed-Loop Workflow

　　Analog signals from the field undergo filtering and A/D conversion via the I/O module before being sent to the high-speed control algorithm layer;

　　The algorithm layer compares the feedback signal with the setpoint to calculate the error; after PID/PI processing and the integration of limiter and PSS correction values, a firing angle command for the rectifier bridge is generated;

　　The firing angle command is transmitted to the FPGA layer, which generates high-precision firing pulses to drive the power rectifier bridge and adjust the excitation current;

　　The resulting excitation current and generator terminal voltage are fed back to the I/O acquisition layer via sensors, completing a main closed-loop cycle; simultaneously, the pulse status is fed back to the FPGA to verify the hardware-level micro-loop;

　　The system monitoring layer monitors the closed-loop operation in real time, responds to external commands to modify control parameters or switch operating modes, and logs operational data.

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