Dc system and control method for variable speed separately excited synchronous generator

Abstract

This invention relates to a DC system and control method for a variable-speed separately excited synchronous generator. It realizes a DC power supply topology consisting of a variable-speed diesel generator set, a three-phase separately excited generator, and a diode rectifier. The variable-speed diesel generator in this system achieves stepless speed regulation. The generator set controller automatically optimizes to the optimal speed point of the diesel generator based on the DC grid load status, solving the problem of controlling the most energy-efficient speed point of the variable-speed diesel generator set. A voltage regulation control algorithm is used to solve the dynamic response problem of a multivariable nonlinear system, ensuring the transient response of the DC grid voltage and solving the problem of stable control of the DC grid voltage under variable-speed conditions. Through load sharing strategies and variable-speed control, the carbon deposit removal function of the variable-speed diesel generator set is achieved. Compared with other DC systems, this invention reduces equipment investment costs, improves the efficiency and reliability of the DC system, and enhances the energy-saving effect of the DC system.

Description

Technical Field

[0001] This invention relates to the field of marine DC power technology, and particularly to a DC system and control method for a variable-speed separately excited synchronous generator. Background Technology

[0002] Currently, most DC-powered ships using diesel engines employ a fixed-speed diesel generator set, asynchronous generator, and controlled rectifier. This topology is costly, requires large space, and has low efficiency across the entire power supply chain, with much energy lost during power transmission, resulting in limited energy savings for DC-powered ships. Another approach uses a fixed-speed diesel generator set, a 12-phase separately excited synchronous generator, and uncontrolled rectifier. This topology uses a 12-phase synchronous generator to reduce voltage pulses on the DC side, but the specially designed generator increases costs. This method reduces control complexity by increasing hardware configuration. Therefore, a low-cost hardware configuration is needed that can achieve not only high-performance DC voltage control but also optimal energy-saving DC system and control method. Summary of the Invention

[0003] To address the energy-saving issue of DC power supply links for ships using diesel engines, a DC system and control method for a variable-speed separately excited synchronous generator is proposed. This system consists of a variable-speed diesel engine, a three-phase separately excited synchronous generator, an excitation device, power diodes, and a generator controller. The variable-speed diesel engine in this system can achieve stepless speed regulation. The generator controller automatically optimizes the diesel engine's speed based on the DC grid load conditions, achieving energy saving and emission reduction. The separately excited synchronous generator is a three-phase generator, eliminating the need to increase the number of generator phases to suppress voltage ripples. During speed regulation of the variable-speed diesel engine or changes in load, the generator controller adjusts the excitation device according to an intelligent control algorithm to stabilize the DC grid voltage, achieving rapid response to the DC grid voltage. The power diodes rectify the generator's AC power into DC power to provide DC power to the grid. Multiple generator units can be networked to achieve carbon buildup reduction.

[0004] The technical solution of the present invention is: a DC system for a variable-speed separately excited synchronous generator, comprising: at least one generator set, each generator set including a variable-speed diesel engine, a three-phase separately excited synchronous generator, an excitation device, a power diode and a generator set controller; The variable-speed diesel engine has stepless speed regulation capability and is used to provide mechanical kinetic energy with adjustable speed. The three-phase separately excited synchronous generator is mechanically connected to the variable speed diesel engine, receives the kinetic energy provided by the variable speed diesel engine and outputs three-phase AC power. The excitation device is connected to the DC excitation interface of the three-phase separately excited synchronous generator and is used to output DC excitation current to control the excitation of the three-phase separately excited synchronous generator. The power diode rectifier is connected to the AC output terminal of the three-phase separately excited synchronous generator and is used to rectify the three-phase AC power into DC power and transmit it to the DC power grid. The generator set controller is electrically connected to the variable-speed diesel engine, the excitation device, the power diode rectifier, and the three-phase separately excited synchronous generator, respectively. The generator set controller collects the AC voltage output by the three-phase separately excited synchronous generator, the DC voltage and DC current output by the power diode rectifier, the excitation feedback signal of the excitation device, and the speed feedback signal of the variable-speed diesel engine. The generator set controller outputs an excitation command to the excitation device and a speed command to the variable-speed diesel engine. The generator controller calculates the optimal energy consumption speed of the variable-speed diesel engine as the operating point based on the DC grid load status using an automatic optimization strategy; the generator controller uses a dual closed-loop control algorithm of outer loop DC voltage and inner loop AC voltage to adjust the excitation device to stabilize the DC grid voltage.

[0005] Preferably, the system consists of multiple generator sets connected in parallel to supply power to the DC grid. The controllers of each generator set communicate with each other, and the controllers distribute the load using a DC voltage droop strategy. The outer-loop DC closed-loop reference voltage value is: DC_REF = DC_RATE (1) –K_VOL ( PWR_REF / PWR_RATE )),in, DC_RATE Set the DC voltage for no-load operation of the unit. K_VOL The droop factor is the DC voltage obtained based on the load. PWR_REF The power reference value assigned to the unit controller, PWR_RATE This refers to the rated power of the unit.

[0006] Preferably, in the DC system of the variable-speed separately excited synchronous generator, when the total grid load exceeds the rated power of a single generator unit, after a designated generator unit activates the carbon deposition elimination function, the generator unit controller adjusts the power distribution among the generator units through power distribution commands. The generator unit that activates the carbon deposition elimination mode operates at its rated speed and rated load, while the remaining generator units operate in variable-speed energy-saving mode. Among these, the voltage droop coefficient of the variable-speed low-load operating generator unit is less than that of the full-load operating generator unit, and load fluctuations are preferentially borne by the variable-speed low-load operating generator unit.

[0007] Preferably, the carbon buildup removal mode runs for a maximum of 60 minutes, after which it automatically exits. A control method for a DC system of a variable-speed separately excited synchronous generator, applied to the DC system, includes the following steps: S1: The generator controller calculates the optimal energy consumption speed of the variable speed diesel engine based on the DC grid load rate using an automatic optimization strategy, and uses it as the operating point of the system. S2: The unit controller adopts a dual closed-loop control algorithm with an outer loop DC voltage and an inner loop AC voltage, and stabilizes the DC grid voltage by adjusting the excitation current of the excitation device; S3: When multiple units are operating in parallel, the controllers of each unit distribute the load through a DC voltage droop strategy.

[0008] Furthermore, the automatic optimization strategy in step S1 specifically includes: S11: In the generator set controller, after normalizing the speed, torque, power, and fuel consumption parameters of the variable-speed diesel engine, design the universal characteristic function of the diesel engine. CharDE ( Load The diesel engine universal characteristic curve, specifically the fuel consumption curve, is expressed in speed step Δ. n Perform digital design; S12: Set the current load of the unit ActLoad Add coefficient LoadCoeff Input to universal property function CharDE ((1 +LoadCoeff ) ActLoad This will generate a series of speeds with equal power but different fuel consumption. Speedeco [ k List, k The value depends on the number of intersections between the current unit's load rate and the average fuel consumption line on the diesel engine's universal characteristic curve. The unit controller... Speedeco [ k Searching the list for the lowest fuel consumption speed point: S121: When multiple fuel consumption speed points exist, the unit controller calculates the difference between these speed points and the current speed. Speedact The absolute values ​​of the differences are taken as the reference point for the operating speed. ; S122: When there is no or only one constant fuel consumption speed point, the unit controller operates at the current speed; S123: LoadCoeff While ensuring the unit can supply the load normally, a 20% margin is reserved to cope with load fluctuations. S13: When the relative load rate of the generator set is greater than the set speed-increasing load rate or lower than the set speed-decreasing load rate, the optimal speed is calculated iteratively using the universal characteristic function based on the current load; the set speed-increasing load rate or the lower than the set speed-decreasing load rate is the percentage of the diesel engine's relative rated power at different speeds.

[0009] Furthermore, the dual closed-loop control algorithm in step S2 specifically includes: The outer loop is a DC closed-loop DC_PID, and the output of the DC closed-loop DC_PID is used as the reference value of the inner loop. The input of the DC closed-loop DC_PID includes the system reference voltage value DC_REF, the DC voltage of the DC bus DC_VOL, and the DC current DC_CUR. The inner loop is an AC closed-loop AC_PID, which uses the fundamental voltage of the AC side output of the three-phase separately excited synchronous generator after FFT transformation as feedback. The input value of the AC closed-loop AC_PID is the difference Error between the output of the outer loop DC closed-loop DC_PID and the feedback of the AC closed-loop AC_PID. The output of the AC closed-loop AC_PID directly drives the excitation device to control the excitation current.

[0010] Furthermore, the unit controller performs Fourier transform on the AC voltage waveform in real time, following the system's reference frequency, and calculates the fundamental voltage in real time. Specifically, the unit controller has a built-in software phase-locked loop (PLL) that captures the zero-crossing frequency of the AC side voltage in real time as the reference frequency. The FFT sampling window adopts an integer-cycle synchronous sampling method, with the number of sampling points fixed at 256 points per cycle. The sampling frequency is automatically adjusted to follow the real-time frequency output by the PLL to ensure that the window length is an integer multiple of the fundamental cycle, thereby avoiding spectral leakage and accurately extracting the fundamental voltage amplitude.

[0011] Furthermore, the AC closed-loop AC_PID employs an adaptive parameter design, specifically including: The speed range of the variable-speed diesel engine is decomposed into N Different speed points Speed [ N For each speed point, further adjustments are made based on the AC closed-loop... AC_PID Input difference Error Difference between input and output Error Differential dError Fuzzy rule base kpRuler [ N ]、 kiRuler [ N ]and kdRuler [ N ]; The activation strength is calculated through fuzzy inference, the outputs of all activated rules are aggregated, and the fuzzification is defuzzified separately using the centroid method. δkp , δki and δkd ; Will δkp , δki and δkd Superimposed on the communication closed loop AC_PID Basic parameters of conventional PID Kp , Ki and KdIn this way, the adaptive dynamic adjustment process of the control system can be realized.

[0012] Furthermore, the reference parameters between the two speed points are linearized using the following formula: Kact = (( Spd act - Spd i ) / ( Spd i+1 - Spd i ))( K i+1 –K i ) + K i Linearization is performed, where, Kact This indicates the reference parameters currently used by the control system; Spd act This indicates the current operating speed of the control system; Spd i Indicates the segmented speed. i Indicates the segmented speed sequence number; K i Indicates the segmented speed point Spd i The baseline PID control parameters; K express Kp, Ki and Kd ; The rule base is selected according to the principle of proximity: Ract = R i Spd act - Spd i ≤ (Spd i+1 - Spd i ) / 2; Ract = R i+1 Spd act - Spd i >(Spd i+1 - Spd i ) / 2; Ract This indicates the rule base currently used by the control system; R i Indicates the segmented speed point Spd iThe corresponding rule base, i This indicates the segmented speed sequence number.

[0013] The beneficial effects of this invention are as follows: The DC system and control method of the variable-speed separately excited synchronous generator of this invention realizes the DC power supply topology of variable-speed diesel generator set, three-phase separately excited generator and diode rectifier. The optimal speed point control of variable-speed diesel generator set is solved by automatic optimization strategy; the stable control of DC grid voltage under variable speed state is solved by intelligent control algorithm; and the carbon deposit removal function of variable-speed diesel generator set is realized by load distribution strategy and variable speed control. The technical solution of this invention reduces the investment cost of equipment, improves the efficiency and reliability of DC system and improves the energy saving effect of DC system. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the DC system architecture for a variable-speed separately excited synchronous generator according to the present invention; Figure 2 This is a schematic diagram of the voltage regulation control algorithm for a variable-speed separately excited synchronous generator according to the present invention. Detailed Implementation

[0015] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0016] like Figure 1The diagram shows a DC system architecture for a variable-speed separately excited synchronous generator. The system consists of several generator sets connected in parallel to supply power to the DC grid. Each generator set includes a variable-speed diesel engine, a three-phase separately excited synchronous generator, an excitation device, a power diode, and a generator controller. The variable-speed diesel engine has stepless speed regulation capability. The separately excited synchronous generator is a three-phase separately excited synchronous generator, and the variable-speed diesel engine provides kinetic energy to the separately excited synchronous generator. After receiving the excitation command from the generator controller, the excitation device outputs a DC excitation current to control the operation of the separately excited synchronous generator. The power diode is a rectifier device, which converts the AC power output from the separately excited synchronous generator into DC power for transmission to the DC grid. The generator controller is the core of the system. The generator controller collects the AC voltage output from the separately excited synchronous generator and the DC voltage and current signals from the output of the rectifier device. It also collects the excitation feedback signal from the excitation device and the speed feedback signal from the variable-speed diesel engine. The generator controller outputs an excitation command to the excitation device and a speed command to the variable-speed diesel engine. The generator controller calculates the optimal energy consumption speed of the variable-speed diesel engine based on the DC grid load rate using an automatic optimization strategy, which serves as the system's operating point. The AC output from the three-phase separately excited synchronous generator, after diode rectification, generates numerous harmonics in the AC circuit. Since the system can operate at different speeds, the fundamental frequency in the AC circuit will dynamically change. The generator controller performs a Fourier transform on the AC voltage waveform in real time, following the system's reference frequency, and calculates the fundamental voltage waveform to achieve closed-loop control of the AC voltage. Because the system's operating speed varies, the impedance of the three-phase separately excited synchronous generator changes accordingly, and the system's dynamic response also differs at different speeds.

[0017] Therefore, a dual-loop control algorithm with outer-loop DC voltage and inner-loop AC voltage was designed to improve the dynamic response and stability of the system. The controllers of each unit communicate with each other, and each controller implements a load distribution strategy through a DC voltage droop strategy: the outer-loop DC closed-loop reference voltage value... DC_REF = DC_RATE (1) –K_VOL ( PWR_REF / PWR_RATE )), DC_RATE Set the DC voltage for no-load operation of the unit. K_VOL The droop factor is the DC voltage obtained based on the load. PWR_REF The power reference value assigned to the unit controller, PWR_RATE This refers to the rated power of the unit.

[0018] When the total grid load exceeds the rated power of a single generating unit, after activating the carbon deposition elimination mode on a designated generating unit, the unit controller... PWR_REFThe power distribution command adjusts the power allocation among the various units. It allows units in activated carbon removal mode to operate at rated speed and load, while the remaining units remain in variable speed energy-saving mode. In this mode, the voltage droop coefficient of the variable speed energy-saving units is less than that of the carbon removal units, and load fluctuations are primarily handled by the variable speed energy-saving units. The maximum continuous operation time for carbon removal mode is limited to 60 minutes, after which it automatically exits. During this period, carbon removal is the primary objective, temporarily sacrificing optimal fuel economy. However, since this accounts for a very small proportion of the operating cycle, its impact on total lifecycle energy consumption is negligible.

[0019] The variable-speed diesel engine is equipped with a speed command and speed feedback interface, which is connected to the unit controller via analog signals. In the unit controller, the universal characteristic function of the diesel engine is designed after normalizing parameters such as speed, torque, power and fuel consumption of the variable-speed diesel engine. Then, the most energy-efficient speed point is calculated through cyclic calculation, so that the system operates under the best conditions.

[0020] The three-phase separately excited synchronous generator is designed with a DC excitation interface, which can output the rated voltage through the excitation device at the lowest speed.

[0021] The power diode module uses water cooling to ensure long-term stable operation of the diodes and rectifies the three-phase AC power into six-pulse DC power to supply the DC power grid.

[0022] The excitation device uses a Basler DECS-250 and operates in FCR mode. The unit controller is connected to the excitation device through an analog interface to directly control the excitation current of the excitation device. This excitation current is connected to the three-phase separately excited synchronous generator through a hard wire to achieve excitation. At the same time, the excitation device feeds back the excitation current to the unit controller through an analog signal for closed-loop control.

[0023] As the core of the system, the unit controller uses a high-speed processing chip with a fastest operating cycle of 10 microseconds. Through its high-speed computing performance, it can perform a fast Fourier transform on the AC side voltage to calculate the fundamental voltage signal, which serves as the feedback input for the AC closed-loop AC_PID.

[0024] The generator set controller automatically optimizes the operation of the variable-speed diesel engine to achieve energy savings based on the DC grid load rate. The specific strategy is as follows: 1) In the generator set controller, after normalizing parameters such as speed, torque, power, and fuel consumption of the variable-speed diesel engine, design the universal characteristic function of the diesel engine. CharDE ( Load The universal characteristic describes the fuel economy of an engine under all stable operating conditions, and its core is the effective fuel consumption rate. b eThe fuel consumption curve, expressed as a function of speed and load, is a function of the universal characteristic curve of a diesel engine with a speed step Δ. n (Take 10) rpm Digital design is performed. 2) Set the current load of the unit ActLoad Add a certain coefficient LoadCoeff Input to universal property function CharDE ((1 +LoadCoeff ) ActLoad This will generate a series of speeds with equal power but different fuel consumption. Speedeco [ k List, k The value depends on the number of intersections between the current unit's load rate and the average fuel consumption line on the diesel engine's universal characteristic curve. The unit controller... Speedeco [ k Searching the list for the lowest fuel consumption speed: A) When multiple fuel-consumption speed points exist, the unit controller calculates the difference between these speed points and the current speed. Speedact The absolute values ​​of the differences are taken as the reference point for the operating speed. B) When there is no or only one constant fuel consumption speed point, the unit controller operates at the current speed; C) LoadCoeff While ensuring the unit can supply the load normally, a 20% margin is reserved to cope with load fluctuations. 3) When the relative load rate of the unit is greater than the set speed-increasing load rate or lower than the set speed-decreasing load rate, the optimal speed is calculated iteratively using the universal characteristic function based on the current load; the set speed-increasing load rate or the lower than the set speed-decreasing load rate is the percentage of the diesel engine's relative rated power at different speeds.

[0025] This system uses a variable-speed diesel engine, meaning the maximum load it can handle varies at different speeds, resulting in a relative rated power at each speed. The acceleration load rate is set at 90% of the relative rated power, and the deceleration load rate is set at 50% of the relative rated power. When the unit load rate is ≥90%, the diesel engine is considered close to the overload point, and the system initiates an upward optimization acceleration after a 10-second delay. When the unit load rate is ≤50%, it is considered to be in a light-load state, and the system initiates a downward optimization deceleration after a 10-second delay. This threshold range is selected to balance the load fluctuation buffer space (preventing frequent triggering of optimization) with the coverage of the diesel engine's universal characteristics and high-efficiency range.

[0026] Because changes in system operating speed cause variations in the impedance of the synchronous generator, and the system's dynamic response differs at different speeds, a dual-closed-loop control algorithm (outer loop DC voltage and inner loop AC voltage) was designed to improve the system's dynamic responsiveness and stability. The specific control strategy is shown below: A) The outer loop is a DC closed loop. DC_PID By collecting data from the DC busbar DC_BUS DC voltage DC_VOL Complete closed-loop control, using the control output as the reference value for the inner loop. DC closed loop. DC_PID The input comes from the system's reference voltage value. DC_ REF DC voltage of DC bus DC_VOL and DC current DC_CUR ,pass DC_VOL and DC_CUR The power of the computer group can be directly measured; B) The inner loop is an AC closed loop. AC_PID, The fundamental voltage obtained by FFT transformation of the AC output voltage of the three-phase separately excited synchronous generator is used as the AC closed loop. AC_PID Feedback, closed-loop communication AC_PID The input value is the outer loop DC closed loop. DC_PID Output and AC closed loop AC_PID The difference between the feedback Error Closed-loop communication AC_PID The output directly drives the excitation device to control the excitation current; Given the dynamic changes in the system's fundamental frequency during variable-speed operation, to ensure the accuracy of FFT calculations, the unit controller incorporates a software phase-locked loop (PLL) to capture the zero-crossing frequency of the AC side voltage in real time as the reference frequency. The FFT sampling window employs an integer-cycle synchronous sampling method, meaning the number of sampling points is fixed at 256 points per cycle. The sampling frequency automatically adjusts to follow the real-time frequency output by the PLL, ensuring the window length is an integer multiple of the fundamental cycle. This effectively avoids spectral leakage and accurately extracts the fundamental voltage amplitude. C) Closed-loop communication AC_PID Medium-parameter adaptive design: The unit controller decomposes the adjustable speed range of the variable-speed diesel engine into... N Different speed points Speed [ N For each speed point, further adjustments are made based on the AC closed-loop... AC_PID Input difference Error Difference between input and output Error Differential dError Fuzzy rule base kpRuler [ N ]、 kiRuler [ N ]and kdRuler [ N The calculation results are defuzzified to generate... δkp , δki and δkd Superimposed on the communication closed loop AC_PID Basic parameters of conventional PID Kp , Kiand Kd In this way, the adaptive dynamic adjustment process of the control system can be realized.

[0027] For example: the generator set controller is configured according to the speed range of the variable-speed diesel engine, 900-1200. rpm It was divided into 4 equal parts. spd 1=900 rpm , spd 2=1000 rpm , spd 3=1100 rpm , spd 4=1200 rpm A baseline is obtained by performing load tests at each speed point. PID parameter Kp spdi , Ki spdi and Kd spdi ( i =1 / 2 / 3 / 4).

[0028] Fuzzification: at the rated speed of 1200 rpm Taking the rotational speed point as an example, record the changes after the load is changed. Error and dError The maximum difference, then Error , dError , δkp , δki and δkd Using triangular membership functions μ ( x Perform blurring processing on each: μ ( x ) = ( x-a ) / ( b-a ) a ≤ x ≤ b ; μ ( x ) = ( c-x ) / ( c-b ) b < x ≤ c ; μ ( x ) = 0x < a,x > c ; in a , b and c These are the three vertices of the triangle.

[0029] As shown in the table below, 1200 rpm The rule base table for time (which combines three rule bases into one table) is used, and the other speed points are designed accordingly. N Indicates negative (-). P Indicates positive (+). B Indicates large (3). M Indicated in (2), S ZO represents small (1) and ZO represents 0.

[0030]

[0031] Fuzzy reasoning: Unit controller based on Error and dError Calculate the membership degree of each input. μ error ( X i )and μ derror ( X i ), traverse all μ error ( X i )and μ derror ( X j The activation strength is obtained as follows: α ruler = Max ij (0, MIN ( μ error ( X i ), μ derror ( X j ))) i ∈[1,7], j ∈[1,7] Apply the activation intensity to the output fuzzy set: μ out ( X k )= Min k ( α ruler , μ out ( X k )) k∈[1,50] The outputs of all activated rules are aggregated: μ agg ( X k )= Max k ( μ out ( X k ), μ agg ( X k k∈[1,50] Calculate μ agg_kp (X k ), μ agg_ki ( X k )and μ agg_kd ( X k ).

[0032] Defuzzification:

[0033]

[0034]

[0035] Calculate separately according to the center of gravity method δkp, δki and δkd, uaggkp i =μ agg_kp ( X k ), uaggki i =μ agg_ki ( X k ), uaggkp i =μ agg_kp ( X k ); outkp i for kp The subdivision of the domain of discourse, i ∈[1,50] outki i for ki The subdivision of the domain of discourse,i ∈[1,50] outkd i for kd The subdivision of the domain of discourse, i ∈[1,50] Control output: Kp= Kp +δkp , Ki= Ki +δki , Kd= Kd +δkd .

[0036] Other speed points are processed in the same manner as above, and the reference parameters between two speed points are as follows: Kact = (( Spd act - Spd i ) / ( Spd i+1 - Spd i ))( K i+1 –K i ) + K i Perform linearization. Kact This indicates the reference parameters currently used by the control system. Kp, Ki, Kp ); Spd act This indicates the current operating speed of the control system; Spd i Indicates the segmented speed. i Indicates the segmented speed sequence number; K i Indicates the segmented speed point Spd i The baseline PID control parameters; K express Kp, Ki and Kd .

[0037] The rule base is selected according to the principle of proximity: Ract = R i , Spd act - Spd i ≤ (Spd i+1 - Spd i ) / 2; Ract = R i+1 , Spd act- Spd i >(Spd i+1 - Spd i ) / 2; Ract This indicates the rule base currently used by the control system; R i Indicates the segmented speed point Spd i The corresponding rule base, i This indicates the segmented speed sequence number.

[0038] The embodiments described above merely illustrate specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A DC system for a variable-speed separately excited synchronous generator, characterized in that, include: At least one generator set, each generator set including a variable-speed diesel engine, a three-phase separately excited synchronous generator, an excitation device, a power diode, and a generator set controller; the variable-speed diesel engine has stepless speed regulation capability and is used to provide mechanical kinetic energy with adjustable speed; the three-phase separately excited synchronous generator is mechanically connected to the variable-speed diesel engine, receives the kinetic energy provided by the variable-speed diesel engine, and outputs three-phase AC power; the excitation device is connected to the DC excitation interface of the three-phase separately excited synchronous generator and is used to output DC excitation current to control the excitation of the three-phase separately excited synchronous generator; the power diode rectifier device is connected to the AC output terminal of the three-phase separately excited synchronous generator and is used to rectify the three-phase AC power into DC power and transmit it to the DC power grid; the generator set controller is connected to the variable-speed diesel engine and the three-phase separately excited synchronous generator controller respectively. The generator, the excitation device, the power diode rectifier, and the three-phase separately excited synchronous generator are electrically connected. The unit controller collects the AC voltage output by the three-phase separately excited synchronous generator, the DC voltage and DC current output by the power diode rectifier, the excitation feedback signal of the excitation device, and the speed feedback signal of the variable-speed diesel engine. The unit controller outputs an excitation command to the excitation device and a speed command to the variable-speed diesel engine. The unit controller calculates the optimal energy consumption speed point of the variable-speed diesel engine as the operating point based on the DC grid load status using an automatic optimization strategy. The unit controller uses a dual closed-loop control algorithm of outer-loop DC voltage and inner-loop AC voltage to adjust the excitation device to stabilize the DC grid voltage.

2. The DC system of the variable-speed separately excited synchronous generator according to claim 1, characterized in that, The system supplies power to the DC grid from multiple generator sets connected in parallel. The controllers of each generator set communicate with each other, and each controller performs load distribution through a DC voltage droop strategy. The outer-loop DC closed-loop reference voltage value is: DC_REF = DC_RATE (1) –K_VOL ( PWR_REF / PWR_RATE )),in, DC_RATE Set the DC voltage for no-load operation of the unit. K_VOL The droop factor is the DC voltage obtained based on the load. PWR_REF The power reference value assigned to the unit controller, PWR_RATE This refers to the rated power of the unit.

3. The DC system of the variable-speed separately excited synchronous generator according to claim 2, characterized in that, When the total grid load exceeds the rated power of a single generating unit, after a designated generating unit activates the carbon deposition elimination function, the unit controller adjusts the power distribution among the generating units through power distribution commands. The generating unit that activates the carbon deposition elimination mode operates at its rated speed and rated load, while the remaining generating units operate in variable speed energy-saving mode. Among these, the voltage droop coefficient of the variable speed low-load operating unit is less than that of the full-load operating unit, and load fluctuations are preferentially borne by the variable speed low-load operating unit.

4. The DC system of the variable-speed separately excited synchronous generator according to claim 3, characterized in that, The carbon buildup removal mode can run for a maximum of 60 minutes, after which it will automatically exit.

5. A control method for a DC system of a variable-speed separately excited synchronous generator, applied to the DC system as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: The unit controller calculates the optimal energy consumption speed of the variable-speed diesel engine based on the DC grid load rate using an automatic optimization strategy, and uses this as the system's operating point. S2: The unit controller adopts a dual closed-loop control algorithm with an outer loop DC voltage and an inner loop AC voltage, and stabilizes the DC grid voltage by adjusting the excitation current of the excitation device. S3: When multiple units are operating in parallel, each unit controller distributes the load using a DC voltage droop strategy.

6. The control method for a DC system of a variable-speed separately excited synchronous generator according to claim 5, characterized in that, The automatic optimization strategy in step S1 specifically includes: S11: After normalizing the speed, torque, power, and fuel consumption parameters of the variable-speed diesel engine in the unit controller, design the universal characteristic function of the diesel engine. CharDE ( Load The diesel engine universal characteristic curve, specifically the fuel consumption curve, is expressed in speed step Δ. n Perform digital design; S12: Set the current load of the unit ActLoad Add coefficient LoadCoeff Input to universal property function CharDE ((1 +LoadCoeff ) ActLoad This will generate a series of speeds with equal power but different fuel consumption. Speedeco [ k List, k The value depends on the number of intersections between the current unit's load rate and the average fuel consumption line on the diesel engine's universal characteristic curve. The unit controller... Speedeco [ k Searching the list for the lowest fuel consumption speed point: S121: When multiple fuel consumption speed points exist, the unit controller calculates the difference between these speed points and the current speed. Speedact The absolute values ​​of the differences are taken as the reference point for the operating speed. S122: When there is no or only one constant fuel consumption speed point, the unit controller operates at the current speed; S123: LoadCoeff Select 0.2 to ensure the unit can supply the load normally, and retain a 20% margin to deal with load fluctuations; S13: When the relative load rate of the unit is greater than the set speed-increasing load rate or lower than the set speed-decreasing load rate, the optimal speed is calculated iteratively by the universal characteristic function based on the current load; the set speed-increasing load rate or the lower than the set speed-decreasing load rate is the percentage of the diesel engine's relative rated power at different speeds.

7. The control method for the DC system of a variable-speed separately excited synchronous generator according to claim 5, characterized in that, The dual closed-loop control algorithm in step S2 specifically includes: an outer loop is a DC closed-loop DC_PID, the output of which serves as the reference value for the inner loop. The inputs of the DC closed-loop DC_PID include the system's reference voltage value DC_REF, the DC bus voltage DC_VOL, and the DC current DC_CUR; the inner loop is an AC closed-loop AC_PID, which uses the fundamental voltage of the AC side output of the three-phase separately excited synchronous generator after FFT transformation as feedback. The input value of the AC closed-loop AC_PID is the difference Error between the output of the outer loop DC closed-loop DC_PID and the feedback of the AC closed-loop AC_PID. The output of the AC closed-loop AC_PID directly drives the excitation device to control the excitation current.

8. The control method for the DC system of the variable-speed separately excited synchronous generator according to claim 7, characterized in that, The unit controller performs Fourier transform on the AC voltage waveform in real time, following the system's reference frequency, and calculates the fundamental voltage in real time. Specifically, the unit controller has a built-in software phase-locked loop (PLL) that captures the zero-crossing frequency of the AC voltage in real time as the reference frequency. The FFT sampling window adopts an integer-cycle synchronous sampling method, with the number of sampling points fixed at 256 points per cycle. The sampling frequency is automatically adjusted to follow the real-time frequency output by the PLL to ensure that the window length is an integer multiple of the fundamental cycle, thereby avoiding spectral leakage and accurately extracting the fundamental voltage amplitude.

9. The control method for the DC system of a variable-speed separately excited synchronous generator according to claim 7, characterized in that, The AC closed-loop AC_PID adopts parameter adaptive design, specifically including: decomposing the speed range of the variable-speed diesel engine into... N Different speed points Speed [ N For each speed point, further adjustments are made based on the AC closed-loop... AC_PID Input difference Error Difference between input and output Error Differential dError Fuzzy rule base kpRuler [ N ]、 kiRuler [ N ]and kdRuler [ N The activation intensity is calculated through fuzzy inference, and the outputs generated by all activated rules are aggregated. Then, the fuzzification is defuzzified using the centroid method, and the activation intensity is calculated separately for each rule. δkp , δki and δkd ;Will δkp , δki and δkd Superimposed on the communication closed loop AC_PID Basic parameters of conventional PID Kp , Ki and Kd In this way, the adaptive dynamic adjustment process of the control system can be realized.

10. The control method for the DC system of a variable-speed separately excited synchronous generator according to claim 9, characterized in that, The reference parameters between the two rotational speed points are linearized using the following formula: Kact = (( Spd act - Spd i ) / ( Spd i+1 - Spd i ))( K i+1 –K i ) + K i Linearization is performed, where, Kact This indicates the reference parameters currently used by the control system; Spd act This indicates the current operating speed of the control system; Spd i Indicates the segmented speed. i Indicates the segmented speed sequence number; K i Indicates the segmented speed point Spd i The baseline PID control parameters; K express Kp, Ki and Kd The rule base is selected based on the principle of proximity: Ract = R i , Spd act - Spd i ≤ (Spd i+1 - Spd i ) / 2; Ract = R i+1 , Spd act - Spd i >(Spd i+1 - Spd i ) / 2; Ract This indicates the rule base currently used by the control system; R i Indicates the segmented speed point Spd i The corresponding rule base, i This indicates the segmented speed sequence number.

Images