Dynamic performance optimization method for ship pulse load power supply system based on virtual capacitance control

Abstract

The invention discloses a method for optimizing the dynamic performance of a ship pulse load power supply system based on virtual capacitance control, and the method can achieve the energy conversion and inertia support of the rotation kinetic energy of a synchronous generator and a DC system capacitor through virtual inertia. A method for calculating a virtual capacitance boundary value under various constraint conditions of considering system stability, dynamic characteristics, parameter coupling and the like is given, and on this basis, according to different functions and energy flow characteristics of a source-side converter and a load-side converter in a power supply system, the virtual capacitance boundary value is calculated; a controllable virtual capacitor control strategy considering both the adjusting capacity and the recovery speed is adopted, and the method effectively improves the transient stability of the system and optimizes the capacitor configuration.

Description

Technical Field

[0001] The present invention provides a system dynamic performance optimization method based on an adaptive virtual capacitor control strategy for a high-power special load power supply structure, specifically involving the energy conversion relationship between the mechanical kinetic energy of a synchronous generator and a DC system and a method for constructing a virtual capacitor, and provides a method for calculating the boundary value of the virtual capacitor under various constraints such as system stability, dynamic characteristics, and parameter coupling, belonging to the field of ship electrical design. Background Art

[0002] In recent years, with the continuous changes in my country's demand for ocean exploration and the development of various types of high-energy exploration equipment and technology, the nonlinear and transient impact characteristics of high-power impact loads are obvious. Due to their special power requirements and operating modes, they have brought severe challenges to the power quality and safety and stability of the power system, especially the ship power system, which is significantly different from the large power grid system. Power electronic devices are the core power conversion units. This type of load has a great impact on the operation of the "limited capacity, strong coupling, and relatively weak" independent power system, including: 1) Due to the long response time of the electromechanical regulation controller of the generator set, the system cannot meet the instantaneous power demand of the pulse load and produce fluctuations or instability; 2) The system presents wide frequency domain and low inertia characteristics, and non-power frequency disturbances may cause subsynchronous interharmonic problems and destroy the stable operation of the system; 3) Deteriorate the power quality of the power grid and interfere with other sensitive loads.

[0003] To solve the above problems, on the one hand, by carrying out the topology optimization of high dynamic response boost / buck converters, the current ripple caused by impact loads is reduced, and the impact of loads on the DC bus in the power supply system is reduced. However, the dynamic behavior of the cascade system is complex, and the lines and control parameters have a great impact on the stability of the system. In addition, there are problems such as large parallel capacitors, inability to adjust, and poor dynamic response performance. On the other hand, in engineering, measures such as increasing the capacity of generator sets are widely used to improve the system's ability to resist impacts. However, due to the lack of in-depth analysis of the system's dynamic characteristics, it is difficult to select diesel generator sets with appropriate power according to the system's operating mode, which may cause excessive configuration of the units and waste resources. In the pulse load power supply system, the isolation of the rectifier decouples the mechanical and electrical parts of the generator set, making it unable to respond to changes in DC voltage. A large amount of inherent mechanical inertia cannot be fully utilized, which reduces the system inertia and makes the transient stability problem more prominent.

[0004] Through the virtual synchronous machine technology, a certain amount of "inertia" is injected into the power grid to resist the fluctuation of load power and buy time for the recovery of power grid faults, effectively supporting the voltage and frequency stability of the system. However, the virtual capacitor control method has not yet been promoted in the field of ship power systems, and there is a lack of calculation methods for the capacitance of different links under multiple constraints that meet the stable operation of the system. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the virtual capacitor control method has not yet been promoted in the field of ship power systems, and there is a lack of calculation methods for the capacitors of different links under multiple constraints that meet the stable operation of the system.

[0006] In order to solve the above technical problems, the technical solution of the present invention is to provide a method for optimizing the dynamic performance of a ship pulse load power supply system based on virtual capacitor control, which is characterized by comprising:

[0007] The energy conversion relationship between the mechanical kinetic energy of the synchronous generator and the DC system and the construction method of the virtual capacitor;

[0008] A method for calculating the boundary value of virtual capacitance is given under various constraints including system stability, dynamic characteristics and parameter coupling.

[0009] According to the different functions of the source converter and the load side converter in the system, the respective virtual capacitor control strategies are given.

[0010] Preferably, the power supply structure of the cascade power supply system is "multi-pulse transformer + uncontrolled rectifier + two-stage interconnected DC / DC converter"; the diesel generator is connected to the medium voltage AC bus, and the pulse load is powered by a system consisting of a 24-pulse phase-shifting transformer, an uncontrolled rectifier, a Buck converter, and a Boost converter multi-stage conversion device; the Buck circuit and the Boost circuit are respectively composed of a filter inductor L1, an input filter capacitor C1, a power switch tube VT1, a freewheeling diode D1 and a filter inductor L2, a power switch tube VT2, an output diode D2, and an output capacitor C2. The Buck output voltage v1 and the Boost output voltage v are controlled by switching the circuit through different duty cycles d. o .

[0011] Preferably, the energy conversion relationship between the mechanical kinetic energy of the synchronous generator and the DC system and the method for constructing the virtual capacitor include:

[0012] In the system, the converter adopts virtual capacitor control. The power absorbed or released by the virtual capacitor and the actual capacitor C jointly bear the fluctuation of the output power, as shown in the following formula:

[0013] (C+C v ) dc du dc / dt=P o +ΔP o +P i

[0014] In the formula, u dc Indicates the DC side voltage;

[0015] The inherent inertia in the system mainly includes the mechanical rotation inertia of the rotor of the diesel generator set on the AC side and the electromagnetic inertia of the capacitor in the DC power grid. k They are

[0016]

[0017] After the generator is rectified uncontrollably, the hidden mechanical kinetic energy of the synchronous generator is released through the virtual capacitor control of the source-side Buck converter to balance the power fluctuations occurring in the next stage together with the inherent capacitance on the output side of the converter. Then:

[0018]

[0019] In the formula, J s 、p n ,ω e They are the moment of inertia, pole pair number and electrical angular velocity of the generator respectively; P m , P e It is divided into the mechanical power and electromagnetic power of the generator; is the per unit value of the change in the electrical angular velocity of the generator; v1, v 1* is the Buck output voltage and its per unit value; C1 is the inherent capacitance of the Buck converter; V 1,ref is the output voltage of Buck converter;

[0020] Preferably, the speed of the generator set and the change of the DC bus voltage in the system need to be within the allowable range of the specification, that is, in, are the upper and lower limits of the per-unit value of the generator electrical angular velocity change, The upper and lower limits of the voltage change at the output side of the Buck converter are:

[0021]

[0022] In the formula, is the steady-state rotor kinetic energy, and is the upper / lower boundary coefficient of the virtual capacitor.

[0023] Preferably, in the method for calculating the boundary value of virtual capacitance under various constraints including system stability, dynamic characteristics and parameter coupling, a large signal average model for closed-loop stability analysis is performed using a mixed potential function. By means of step-by-step equivalence, the voltage and current variables at each level of the system are linked through a power balance relationship to obtain a large signal stability criterion in an analytical form.

[0024] Preferably, a large signal average model based on hybrid potential function stability analysis is adopted, the pulse load side converter adopts closed-loop control, and the closed-loop response speed is much faster than the source side converter, and the pulse load and the Boost converter are equivalent to a constant power load together, then:

[0025] The mixed potential function of the interconnected system is

[0026]

[0027] The third stability theorem of mixed potential function theory is used to analyze the large perturbation stability of the system.

[0028] Then we have:

[0029]

[0030] Assuming that the load power increases suddenly and its energy is fully supplemented by the supporting capacitor, we have:

[0031]

[0032] In the formula, and δ are the Buck converter response time constant and the filter inductor allowable pulsating current coefficient, respectively, and we can obtain:

[0033] In the formula, It represents the proportional parameter of the PI link of the Buck converter voltage loop. represents the integral parameter of the PI link of the Buck converter voltage loop, v 1,ref Indicates the output voltage setting value of the Buck converter, represents the proportional parameter of the PI link of the Buck converter current loop, R1 represents the parasitic resistance of the Buck converter inductor, v i Indicates the voltage on the input side of the Buck converter.

[0034] Preferably, the load-side converter adopts a voltage and current dual closed-loop control method, and the control loop equation and state equation are as follows:

[0035]

[0036] In the formula, represents the given value of the inner loop current of the Boost converter, It represents the proportional parameter of the PI link of the Boost converter voltage loop. represents the integral parameter of the PI link of the Boost converter voltage loop, v o,ref represents the output voltage setting value of the Boost converter, d2 represents the duty cycle of the Boost converter, It represents the proportional parameter of the PI link of the Boost converter current loop. represents the integral parameter of the PI link of the Boost converter current loop, L2 represents the inductance of the Boost converter, represents the inductor current of the Boost converter, represents the Boost converter inductor parasitic resistance, represents the Boost converter capacitor current, represents the capacitor parasitic resistance, and C2 represents the Boost converter capacitor.

[0037] Get the mixed potential function of the Boost link:

[0038]

[0039] Then we have:

[0040]

[0041] L and C are the diagonal matrices of the inductor and capacitor components in the circuit, respectively. The smallest characteristic root μ1 of the matrix The minimum characteristic root μ2 of , we get: According to μ1+μ2>0, the boundary of the load-side converter output capacitance is derived as follows:

[0042] Preferably, the virtual capacitor control strategy includes a source-side converter virtual capacitor control strategy and a load-side converter virtual capacitor control strategy.

[0043] Preferably, in the source side converter virtual capacitance control strategy:

[0044] The virtual capacitor control of the source-side Buck converter can release the hidden mechanical kinetic energy of the synchronous generator. The energy equivalence relationship of the output-side capacitor is expressed as:

[0045]

[0046] Where W Buck represents the Buck converter capacitor energy, p n represents the number of synchronous generator pole pairs, ω e represents the electrical angular velocity of the synchronous generator;

[0047] Get the virtual equivalent inertia J of the output side of the source side Buck converter eq_1

[0048]

[0049] In the formula, J s represents the moment of inertia of the synchronous generator, E k represents the rotational kinetic energy of the synchronous generator;

[0050] Changing the inertia equivalent coefficient To realize the controllable inertia control of the source side converter: The relationship between the equivalent capacitance and the actual capacitance of the source-side converter output side is derived: C eq_1 =C1+C v_1 =ξ Buck C1, where C v_1 is the virtual capacitance of the source side converter, and the inertia equivalent coefficient ξ Buck The value range of is:

[0051]

[0052] In the formula, E k0 represents the steady-state rotor kinetic energy.

[0053] Preferably, in the load-side converter virtual capacitor control strategy:

[0054] The DC voltage change (△v o =v o.ref -v o ) and voltage change rate (dv o / dt) are introduced into the adjustment of virtual capacitance: 1) When the power deviation increases, △v o *dv o / dt>0, first improve the rapidity of voltage action, then suppress voltage fluctuations; 2) When the power deviation decreases, △v o *dv o / dt<0, the voltage deviation will change in a small direction and tend to be stable, and rapid adjustment is performed at this time;

[0055] C0 is the steady-state value of the virtual capacitor; c and d are the control parameters of each item; l is the adjustment threshold, then the adaptive virtual capacitor C v_2 for:

[0056] The present invention discloses a method for optimizing the dynamic performance of a ship pulse load power supply system based on virtual capacitor control. The method can convert the rotational kinetic energy of a synchronous generator into energy and inertia support between the capacitor of a DC system through virtual inertia, and provides a method for calculating the boundary value of the virtual capacitor under various constraints such as system stability, dynamic characteristics and parameter coupling. On this basis, according to the different functions and energy flow characteristics of the source-side converter and the load-side converter in the power supply system, controllable virtual capacitor control strategies that take both regulation capability and recovery speed into consideration are adopted. The method effectively improves the transient stability of the system and optimizes the capacitor configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The topology of the complex cascade system is illustrated;

[0058] Figure 2 The virtual capacitor control principle is illustrated;

[0059] Figure 3 is the equivalent circuit of the interconnected system;

[0060] Figure 4 The virtual inertia control strategy of the source side converter is illustrated;

[0061] Figure 5 The virtual capacitor control strategy of the load-side converter is illustrated;

[0062] Figure 6 The AC system frequency response is shown. DETAILED DESCRIPTION

[0063] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0064] A method for optimizing the dynamic performance of a ship pulse load power supply system based on virtual capacitor control disclosed in an embodiment of the present invention specifically includes the following steps:

[0065] 1. Energy conversion relationship between mechanical kinetic energy of synchronous generator and DC system and construction method of virtual capacitor

[0066] The power supply structure of the cascade power supply system is "multi-pulse transformer + uncontrolled rectifier + two-stage interconnected DC / DC converter". It has multiple AC / DC conversion links, including multiple series and parallel cascades. The diesel generator is connected to the medium-voltage AC bus and supplies power to the pulse load through a system composed of a 24-pulse phase-shifting transformer, an uncontrolled rectifier, a Buck converter, and a Boost converter. Figure 1 As shown in the figure. The Buck circuit and Boost circuit are composed of filter inductor L1, input filter capacitor C1, power switch tube VT1, freewheeling diode D1 and filter inductor L2, power switch tube VT2, output diode D2, and output capacitor C2 respectively. The Buck output voltage v1 and Boost output voltage v are controlled by switching the circuit with different duty cycles d. o .

[0067] Figure 2 In, P i ,I i are respectively the active power and current flowing to the capacitor from the previous converter; P o ,I o They are respectively the active power and current transmitted to the next level; C V is the virtual capacitor; P V It is the power absorbed or released by the virtual capacitor. The converter power flows to the next stage as the positive direction.

[0068] In the system, the converter adopts virtual capacitor control. The power absorbed or released by the virtual capacitor and the actual capacitor C jointly bear the fluctuation of the output power:

[0069] (C+C v ) dc du dc / dt=P o +ΔP o +P i (1)

[0070] In the formula, u dc Indicates the DC side voltage.

[0071] The inherent inertia in the system mainly includes the mechanical rotation inertia of the rotor of the diesel generator set on the AC side and the electromagnetic inertia of the capacitor in the DC power grid. k They are

[0072]

[0073] After the generator has been rectified uncontrollably, the hidden mechanical kinetic energy of the synchronous generator can be released through the virtual capacitor control of the source-side Buck converter to balance the power fluctuations occurring in the next stage together with the inherent capacitance on the converter output side. Then:

[0074]

[0075] In the formula, J s 、p n ,ω e They are the moment of inertia, pole pair number and electrical angular velocity of the generator respectively; P m , P e It is divided into the mechanical power and electromagnetic power of the generator; is the per unit value of the change in the electrical angular velocity of the generator; v1, v 1* is the Buck output voltage and its per unit value; C1 is the inherent capacitance of the Buck converter; V 1,ref is the Buck converter output voltage.

[0076] The speed of the generator set and the change of DC bus voltage in the system must be within the allowable range of the specification, that is, in, are the upper and lower limits of the per-unit value of the generator electrical angular velocity change, are the upper and lower limits of the voltage change at the output side of the Buck converter, and we can get:

[0077]

[0078] In the formula, is the steady-state rotor kinetic energy, and is the upper / lower boundary coefficient of the virtual capacitor.

[0079] 2. System stability criteria

[0080] The mixed potential function P can be written in the following unified form: P(i,v) = -A(i) + B(v) + (i,γv-α), where: i,v are the inductor current and capacitor voltage in the circuit respectively; A(i) is the current potential function of the non-energy storage element in the nonlinear circuit; B(v) is the voltage potential function of the non-energy storage element in the circuit; (i,γv-α) is the voltage-current product of the capacitor and other non-energy storage elements. The third stability theorem of the mixed potential function theory is used to analyze the large perturbation stability of the system, which can be restated as follows:

[0081]

[0082] L and C are the diagonal matrices of inductance and capacitance in the circuit, respectively.

[0083]

[0084] If all currents and voltages in the system can meet And when |i|+|v|→∞, there is a Lyapunov type function P* (i,v)→∞, that is, when t→∞, all solutions will tend to the steady-state value and the system will tend to a steady state, which can ensure the stability of the system under large disturbances.

[0085] When the load fluctuates over a large range, the nonlinearity of the power electronic devices and control loops in the system makes the description of the duty cycle very complicated. The present invention adopts a large signal average model based on the stability analysis of the mixed potential function. The pulse load side converter adopts closed-loop control, and the closed-loop response speed is much faster than the source side converter. Therefore, the pulse load and the Boost converter can be equivalent to a constant power load. The equivalent circuit of the interconnected system is as follows: Figure 3 shown.

[0086] The mixed potential function of the interconnected system is

[0087]

[0088] Where i1 is the Buck output current, i n is an equivalent current source.

[0089] Derivatives of current and voltage are obtained:

[0090]

[0091] Where, L ρ and i ρ represents the ρth inductor and its current, C σ and U σ Represents the σth capacitor and its voltage.

[0092] Next, we obtain the variable A in formula (9): ii With B vv :

[0093]

[0094] Then we have:

[0095]

[0096] The source side converter adopts the voltage and current double closed-loop control method, and the control loop equation is:

[0097]

[0098] In the formula, represents the given value of the inner loop current of the Buck converter, It represents the proportional parameter of the PI link of the Buck converter voltage loop. represents the integral parameter of the PI link of the Buck converter voltage loop, v 1,refrepresents the output voltage setting value of the Buck converter, d1 represents the duty cycle of the Buck converter, It represents the proportional parameter of the PI link of the Buck converter current loop. represents the inductor current of the Buck converter, It represents the integral parameter of the PI link of the Buck converter current loop.

[0099] According to the KCL and KVL theorems, the state equation of the Buck circuit is as follows:

[0100]

[0101] Where L1 represents the inductance of the Buck converter. represents the inductor current of the Buck converter, R1 represents the parasitic resistance of the inductor of the Buck converter, v , Indicates the voltage on the input side of the Buck converter. represents the Buck converter capacitor current, Represents the Buck converter capacitance.

[0102] From the above formula (9), we can get:

[0103]

[0104] in, (N is a constant) is a time variable and has no effect on the partial differential, so:

[0105]

[0106] according to P load Represents the load power, and can be deduced:

[0107]

[0108] Combining equations (7), (11) and (12), μ1+μ2>0, it can be written as:

[0109]

[0110] Assuming that the load power increases suddenly and its energy is fully supplemented by the supporting capacitor, then

[0111]

[0112] In the formula, and δ are the response time constant of the Buck converter and the allowable pulsating current coefficient of the filter inductor, respectively. From formula (13), we can get:

[0113]

[0114] Similarly, the load-side converter also uses a voltage and current dual closed-loop control method. The control loop equation and state equation are as follows:

[0115]

[0116]

[0117] In the formula, represents the given value of the inner loop current of the Boost converter, It represents the proportional parameter of the PI link of the Boost converter voltage loop. represents the integral parameter of the PI link of the Boost converter voltage loop, v o,ref represents the output voltage setting value of the Boost converter, d2 represents the duty cycle of the Boost converter, It represents the proportional parameter of the PI link of the Boost converter current loop. represents the integral parameter of the PI link of the Boost converter current loop, L2 represents the inductance of the Boost converter, represents the inductor current of the Boost converter, represents the Boost converter inductor parasitic resistance, represents the Boost converter capacitor current, represents the capacitor parasitic resistance, and C2 represents the Boost converter capacitor.

[0118] The mixed potential function of the Boost link can be written as:

[0119]

[0120] Then we have:

[0121]

[0122] Solve the matrices separately The smallest characteristic root μ1 of the matrix The minimum characteristic root μ2 of , we get: According to μ1+μ2>0, the boundary of the load-side converter output capacitance is derived as follows:

[0123]

[0124] 3. Virtual capacitor control strategy

[0125] By adaptively controlling the inertia, the stability of the system is ensured, while taking into account the rapidity of the system. The DC network part of this system adopts a two-stage DC converter interconnection structure. The front-stage converter allows a certain fluctuation in the output voltage to achieve the average current part of the current caused by the input current following the pulse load. The intermediate capacitor balances the power fluctuation generated by the load. The rear-stage converter controls the stability of the output voltage to ensure high-precision power supply of the pulse load and smooth the impact of the pulse load on the AC side. The converters on the source side and the load side realize different functions respectively, so their control strategies are also different.

[0126] 3.1 Source-side converter virtual capacitor control strategy

[0127] The virtual capacitor control of the source-side Buck converter can release the hidden mechanical kinetic energy of the synchronous generator, and the energy equivalence relationship of the output-side capacitor can be expressed as:

[0128]

[0129] Where W Buck represents the Buck converter capacitor energy, p n represents the number of synchronous generator pole pairs, ω e Represents the electrical angular velocity of the synchronous generator.

[0130] The equivalent inertia J virtualized on the output side of the source side Buck converter can be obtained eq_1

[0131]

[0132] In the formula, J s represents the moment of inertia of the synchronous generator, E k Represents the rotational kinetic energy of the synchronous generator.

[0133] Therefore, the inertia equivalent coefficient can be changed To realize the controllable inertia control of the source side converter. The relationship between the equivalent capacitance and the actual capacitance of the source-side converter output side can be derived: C eq_1 =C1+C v_1 =ξ Buck C1, where C v_1 is the virtual capacitor of the source side converter. Combining equation (3) and equation (16), the inertia equivalent coefficient ξ can be obtained Buck The value range of is:

[0134]

[0135] In the formula, E k0 represents the steady-state rotor kinetic energy.

[0136] Considering the allowable range of the generator speed change and DC voltage fluctuation, as well as the transient stability of the system, the inner loop reference current adds a virtual inertia adaptive control compensation link to change the power output of the source side converter. The control strategy is as follows Figure 4 In the initial stage of frequency change, a larger virtual inertia can effectively prevent the frequency change. In the subsequent frequency recovery period, a smaller inertial response can quickly restore the frequency to stability and shorten the system oscillation time.

[0137] 3.2 Load-side converter virtual capacitor control strategy

[0138] Pulse load frequency operation will cause the DC bus voltage to fluctuate violently, seriously affecting the power quality of the DC voltage. The requirement for high-precision power supply to the load makes the allowable range of voltage fluctuation on the output side of the load-side converter very small. Therefore, a large capacitor needs to be configured to ensure the normal operation of the load. The actual capacitance value is generally constant and cannot be adjusted. The larger the capacitance value, the longer the DC voltage recovery time. In actual engineering applications, the load-side converter capacitance is about 10 times that of the source-side converter capacitance, and there is an unreasonable configuration problem of "top-heavy". In order to better suppress the fluctuation of the load-side DC bus voltage, optimize the dynamic response, and solve the problem of excessive load-side converter capacitance, the present invention adopts a variable virtual capacitor control strategy to simulate the characteristics of the capacitor so that the bus voltage response has controllable dynamic performance. The control strategy is as follows: Figure 5 shown.

[0139] The DC voltage change (△v o =v o.ref -v o ) and voltage change rate (dv o / dt) are introduced into the adjustment of virtual capacitance: 1) When the power deviation increases, △v o *dv o / dt>0, first improve the rapidity of voltage action, then suppress voltage fluctuations; 2) When the power deviation decreases, △v o *dv o / dt<0, the voltage deviation will change in a small direction and tend to be stable, and rapid adjustment is required at this time. v_2 is the virtual capacitance value, C0 is its steady-state value, which is obtained by formula (22); c, d are the control parameters of each item respectively; l is the adjustment threshold, then the adaptive virtual capacitance is

[0140]

[0141] For a type of integrated monitoring ship equipped with a phased array radar, the radar power supply structure is as follows: Figure 1 As shown. The peak power of the phased array radar P L=300kW, duty cycle D = 0.4, period T = 30ms; power station generator set U G =6600V, rated power P G =400kW, frequency f G =50Hz; rated DC voltage at output side of 24-pulse uncontrolled rectifier v i =710V; Buck converter output side rated DC voltage v1 = 510V, capacitor C1 = 30μF and 47μF inductor L1 = 200μH, Boost converter output side rated DC voltage v o =710V, capacitor C2 = 0.005F and 0.055F, inductor L2 = 60μH, The switching frequency of the converter is 6.4kHz. The following three control modes are set: Mode 1 is C1 = 30μF, C2 = 0.005F, the source side and load side converters use ordinary dual-loop control; Mode 2 is C1 = 47μF, C2 = 0.055F, the source side and load side converters use ordinary dual-loop control; Mode 3 is C1 = 2500μF, C2 = 0.005F, and both the source side and load side converters use controllable virtual capacitor control.

[0142] Figure 6 The frequency response waveform of the AC side under different control modes. When the pulse load is put into operation for 0.2s, the larger the capacitance value of each level of conversion link in the DC power grid is, the higher the charging power is. A large amount of power impact will cause the generator speed to drop sharply. Therefore, the frequency transient drop of control mode 1 is smaller than that of control mode 2, and it recovers to a stable state faster. Under the action of inertia control, control mode 3 enables the source side converter to release the kinetic energy stored in the generator to increase the output power, provide initial power support for the system, compensate for the system power shortage, and suppress the sudden change of the DC side voltage. As the voltage change speed slows down, the generator output power gradually and steadily recovers to the rated value, and the average power of the pulse load is output stably. The mechanical inertia of the AC system is released through virtual capacitor control, and a controllable virtual inertia is virtualized in the DC power grid, thereby effectively improving the transient stability of the DC voltage and reducing the impact of the pulse load on the AC side.

[0143] The load startup moment will have a huge impact on the DC power grid, and quickly extract energy from the energy storage element in the load-side converter. The pulsating part of the current caused by the pulse load is shared by the output capacitor and the filter inductor. If the pulsation of the input current of the power supply system is to be reduced as much as possible, the current flowing through the inductor needs to be controlled to follow the average current in the current caused by the pulse load, and the pulsating current part is provided by the output capacitor branch as much as possible. From the output voltage response waveform of the load-side converter, it can be seen that a larger fixed capacitor can effectively reduce the temporary drop and steady-state fluctuation of the bus voltage, but overshoot will occur, which is not conducive to system stability. The controllable virtual capacitor control strategy proposed in this paper can make the voltage response curve have a larger change rate at the beginning of the load change, and adjust the size of the virtual capacitor with the later voltage change rate to make the curve accelerate and stabilize, without overshoot, and reduce the adjustment time. The adaptive virtual capacitor control can adjust the virtual capacitor value bidirectionally according to the load-side voltage change to increase or decrease to suppress voltage fluctuations and provide rapid voltage recovery.

[0144] The average current part of the current caused by the source side converter with the pulse load, under the ordinary dual-loop inertia-free control, the instantaneous power impact transmitted by the load side converter when the load starts causes the DC voltage to drop to a certain extent. After the virtual inertia control, the energy storage element of the source side converter virtualizes a large virtual inertia, which provides support for the system voltage, significantly reducing its drop amplitude and change rate, and adjusting the size of the virtual inertia to make the curve accelerate and tend to be stable. When the load is switched, the energy storage element virtualizes a large virtual inertia, which has a more obvious effect on suppressing the sudden change of the DC side voltage, and the transient voltage change process is more gentle. In addition, it provides inertia support for the system, which significantly reduces the frequency drop and change rate of the AC system. In the recovery stage, the small inertia can make the system enter stability faster, taking into account the adjustment ability and recovery speed. Moreover, under the virtual inertia control, the variable power of the generator set provides long-lasting and gentle power support to the DC power grid, reducing the voltage steady-state change amplitude, so that the inherent mechanical inertia reserve of the AC system is fully utilized.

[0145] The present invention discloses a method for optimizing the dynamic performance of a high-power special load power supply system based on an adaptive virtual capacitor control strategy, which belongs to the field of ship electrical design. The method can convert the rotational kinetic energy of a synchronous generator into energy and inertia support between the capacitor of a DC system through virtual inertia, and considers the calculation of the virtual capacitor boundary value under various constraints such as system stability, dynamic characteristics, and parameter coupling. On this basis, according to the different functions and energy flow characteristics of the source-side converter and the load-side converter in the power supply system, a controllable virtual capacitor control strategy that takes both regulation capability and recovery speed into consideration is adopted to effectively improve the transient stability of the system and optimize the capacitor configuration.

Claims

1. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control, characterized in that: include: The energy conversion relationship between the mechanical kinetic energy of the synchronous generator and the DC system and the construction method of the virtual capacitor; A method for calculating the boundary value of virtual capacitance is given under various constraints including system stability, dynamic characteristics and parameter coupling. According to the different functions of the source converter and the load side converter in the system, the respective virtual capacitor control strategies are given.

2. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control as claimed in claim 1, characterized in that: The power supply structure of the cascade power supply system is "multi-pulse transformer + uncontrolled rectifier + two-stage interconnected DC / DC converter"; the diesel generator is connected to the medium-voltage AC bus, and the pulse load is powered by a system composed of a 24-pulse phase-shifting transformer, an uncontrolled rectifier, a Buck converter, and a Boost converter. The Buck circuit and the Boost circuit are respectively composed of a filter inductor L1, an input filter capacitor C1, a power switch tube VT1, a freewheeling diode D1 and a filter inductor L2, a power switch tube VT2, an output diode D2, and an output capacitor C2. The Buck output voltage v1 and the Boost output voltage vo are controlled by switching the circuits with different duty cycles d.

3. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control as claimed in claim 2, characterized in that: The energy conversion relationship between the mechanical kinetic energy of the synchronous generator and the DC system and the construction method of the virtual capacitor include: In the system, the converter adopts virtual capacitor control. The power absorbed or released by the virtual capacitor and the actual capacitor C jointly bear the fluctuation of the output power, as shown in the following formula: (C+C v )u dc travel dc / dt=P o +ΔP o +P i In the formula, u dc Indicates the DC side voltage; After the generator is rectified uncontrollably, the hidden mechanical kinetic energy of the synchronous generator is released through the virtual capacitor control of the source-side Buck converter to balance the power fluctuations occurring in the next stage together with the inherent capacitance on the output side of the converter. Then: In the formula, J s 、p n ,ω e They are the moment of inertia, pole pair number and electrical angular velocity of the generator respectively; P m , P e It is divided into the mechanical power and electromagnetic power of the generator; is the per unit value of the change in the electrical angular velocity of the generator; v1, v 1* is the Buck output voltage and its per unit value; C1 is the inherent capacitance of the Buck converter; V 1,ref is the Buck converter output voltage.

4. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control as claimed in claim 3, characterized in that: The speed of the generator set and the change of DC bus voltage in the system must be within the allowable range of the specification, that is, in, are the upper and lower limits of the per-unit value of the generator electrical angular velocity change, The upper and lower limits of the voltage change at the output side of the Buck converter are obtained: In the formula, is the steady-state rotor kinetic energy, and is the upper / lower boundary coefficient of the virtual capacitor.

5. The method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control according to claim 1, characterized in that: In the method for calculating the boundary value of virtual capacitance under various constraints including system stability, dynamic characteristics and parameter coupling, a large signal average model for closed-loop stability analysis is performed using a mixed potential function. By means of step-by-step equivalence, the voltage and current variables at each level of the system are linked through a power balance relationship to obtain a large signal stability criterion in an analytical form.

6. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control as claimed in claim 5, characterized in that: The large signal average model based on the hybrid potential function stability analysis is adopted. The pulse load side converter adopts closed-loop control, and the closed-loop response speed is much faster than the source side converter. The pulse load and the Boost converter are equivalent to a constant power load. Then: The mixed potential function of the interconnected system is Applying the third stability theorem of mixed potential function theory to analyze the large disturbance stability of the system, we have: Assuming that the load power increases suddenly and its energy is fully supplemented by the supporting capacitor, we have: In the formula, and δ are the Buck converter response time constant and the filter inductor allowable pulsating current coefficient, respectively, and we can obtain:

7. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control as claimed in claim 5, characterized in that: The load-side converter adopts a voltage and current dual closed-loop control method. The control loop equation and state equation are as follows: In the formula, represents the given value of the inner loop current of the Boost converter, It represents the proportional parameter of the PI link of the Boost converter voltage loop. represents the integral parameter of the PI link of the Boost converter voltage loop, v o,ref represents the output voltage setting value of the Boost converter, d2 represents the duty cycle of the Boost converter, It represents the proportional parameter of the PI link of the Boost converter current loop. represents the integral parameter of the PI link of the Boost converter current loop, L2 represents the inductance of the Boost converter, represents the inductor current of the Boost converter, represents the Boost converter inductor parasitic resistance, represents the Boost converter capacitor current, represents the capacitor parasitic resistance, and C2 represents the Boost converter capacitor. Get the mixed potential function of the Boost link: Then we have: Solve the matrices separately The smallest characteristic root μ1 of the matrix The minimum characteristic root μ2 of , we get: According to μ1+μ2>0, the boundary of the load-side converter output capacitance is derived as follows:

8. The method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control according to claim 2, characterized in that: The virtual capacitor control strategy includes a source side converter virtual capacitor control strategy and a load side converter virtual capacitor control strategy.

9. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control as claimed in claim 8, characterized in that: In the source side converter virtual capacitor control strategy: The virtual capacitor control of the source-side Buck converter can release the hidden mechanical kinetic energy of the synchronous generator. The energy equivalence relationship of the output-side capacitor is expressed as: Where W Buck represents the Buck converter capacitor energy, p n represents the number of synchronous generator pole pairs, ω e represents the electrical angular velocity of the synchronous generator; Get the virtual equivalent inertia J of the output side of the source side Buck converter eq_1 In the formula, J s represents the moment of inertia of the synchronous generator, E k represents the rotational kinetic energy of the synchronous generator; Changing the inertia equivalent coefficient To realize the controllable inertia control of the source side converter: The relationship between the equivalent capacitance and the actual capacitance of the source-side converter output side is derived: C eq_1 =C1+C v_1 =ξ Buck C1, where C v_1 is the virtual capacitance of the source side converter, and the inertia equivalent coefficient ξ Buck The value range of is: In the formula, E k0 represents the steady-state rotor kinetic energy.

10. A method for optimizing dynamic performance of a ship pulse load power supply system based on virtual capacitor control as claimed in claim 8, characterized in that: In the load-side converter virtual capacitor control strategy: The DC voltage change (△v o =v o.ref -v o ) and voltage change rate (dv o / dt) are introduced into the adjustment of virtual capacitance: 1) When the power deviation increases, △v o *dv o / dt>0, first improve the rapidity of voltage action, then suppress voltage fluctuations; 2) When the power deviation decreases, △v o *dv o / dt<0, the voltage deviation will change in a small direction and tend to be stable, and rapid adjustment is performed at this time; C0 is the steady-state value of the virtual capacitor; c and d are the control parameters of each item; l is the adjustment threshold, then the adaptive virtual capacitor C v_2 for:

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