Novel low-voltage multi-port single-phase power supply equipment control method

Abstract

The invention relates to the technical field of power distribution network management, in particular to a novel low-voltage multi-port single-phase power supply equipment control method. Comprising the steps that novel low-voltage single-phase multi-port power supply equipment composed of an AC / DC converter, three DC / AC converters and a middle direct-current bus is constructed; firstly, a Vdc-Q control mode is adopted to carry out DC bus voltage control, secondly, a Vf virtual synchronous machine control mode is adopted to carry out single-phase voltage frequency control, and finally, single-phase source network load storage coordinated optimization control is carried out. According to the design, independent control over power supply of the phases A, B and C in the three phases is achieved through the electric power technology and equipment, safe and reliable power supply of the phases is guaranteed, and meanwhile multi-main-body optimization among distributed photovoltaic, energy storage and loads can be achieved; the electric energy quality problems of three-phase imbalance, harmonic waves, voltage fluctuation and flicker and the like of a low-voltage three-phase line can be fundamentally solved through direct-current bus isolation, and the electric energy quality management system has outstanding advantages in the aspects of electric energy quality management effect and management cost.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution network management, and in particular to a novel low-voltage multi-port single-phase power supply equipment control method. Background Art

[0002] With the accelerated transformation of the country's energy cleanliness, wind power generation and photovoltaic power generation have been increasingly widely used. A large number of distributed photovoltaics are connected to low-voltage distribution networks, especially low-voltage single-phase distribution networks. Power quality problems such as high / low voltage, three-phase imbalance, voltage fluctuations and flicker, and harmonics are more prominent, seriously affecting the safe and high-quality power supply of low-voltage distribution networks.

[0003] For high / low voltage problems, on-load tap-changing transformers and reactive power compensation are traditionally used for regulation; for three-phase imbalance, phase-changing switches are mainly used to change the load access phases to improve the three-phase imbalance; voltage fluctuations, flickers, and harmonics are mainly solved by active power filters, dynamic voltage restorers, etc. However, these methods still have technical deficiencies, such as:

[0004] First, for high / low voltage problems, on-load tap-changing transformers and reactive power compensation are traditionally used for regulation. However, both on-load tap-changing transformers and reactive power compensation are discretely regulated and cannot be adjusted continuously. In addition, the service life of the equipment is affected by the number of adjustments.

[0005] Secondly, to solve the three-phase imbalance problem, the phase-changing switch is mainly used to change the load access phase to improve the three-phase imbalance. However, the phase-changing switch can only partially solve the three-phase imbalance problem, but not completely, and there are risks such as phase short circuit and short-term power supply interruption.

[0006] Third, problems such as voltage fluctuation, flicker and harmonics are mainly solved by active power filters, dynamic voltage restorers, etc., which have the problems of single function and large equipment investment.

[0007] In general, traditional methods are single solutions to single problems, and the results are still not ideal, with deficiencies in technical performance, cost and life. In view of this, in order to solve the problem of safe and high-quality power supply in low-voltage distribution networks, especially the power quality problems such as high / low voltage, three-phase imbalance, voltage fluctuation and flicker, and harmonics after a large number of distributed photovoltaics are connected to low-voltage distribution networks, we propose a new low-voltage multi-port single-phase power supply equipment control method. Summary of the invention

[0008] The purpose of the present invention is to provide a novel low-voltage multi-port single-phase power supply equipment control method to solve the problems raised in the above background technology.

[0009] In order to solve the above technical problems, the purpose of the present invention is to provide a novel low-voltage multi-port single-phase power supply equipment control method. First, a novel low-voltage single-phase multi-port power supply equipment consisting of an AC / DC converter, three DC / AC converters and a DC bus in the middle is constructed; the control method comprises the following steps:

[0010] S1. DC bus voltage control: The DC bus voltage control of the new low-voltage multi-port single-phase power supply refers to the AC / DC converter adopting the Vdc-Q control mode, where Vdc is the DC bus voltage and Q is the total reactive power of the three-phase four-wire incoming line; the Vdc-Q control mode means that the AC / DC converter controls the DC bus voltage and the total reactive power of the three-phase four-wire incoming line at the same time;

[0011] S2. Single-phase voltage and frequency control: The single-phase voltage and frequency control of the new low-voltage multi-port single-phase power supply refers to the DC / AC converter adopting the Vf virtual synchronous machine control mode, where V is the single-phase AC voltage output by the DC / AC converter, and f is its frequency; the Vf virtual synchronous machine control mode means that the DC / AC converter controls the single-phase AC voltage and frequency it outputs to ensure the power supply of the load connected to the phase line and the consumption of photovoltaic power;

[0012] S3. Single-phase source-grid-load-storage coordinated optimization control: The single-phase source-grid-load-storage coordinated optimization control of the new low-voltage multi-port single-phase power supply refers to the coordinated optimization control between the DC / AC converter and the distributed photovoltaic and energy storage connected to the single-phase line it supplies power. Its goal is to ensure that the DC / AC converter is not overloaded and to maximize the benefits of multiple distributed photovoltaic and energy storage entities.

[0013] As a further improvement of the technical solution, in the novel low-voltage single-phase multi-port power supply device, one AC / DC converter is simultaneously connected and energy-exchanged with three DC / AC converters via a DC bus.

[0014] As a further improvement of the technical solution, in step S1, the specific control strategy of the DC bus voltage control is as follows:

[0015] The Vdc-Q control mode adjusts the active power of the AC / DC converter according to the deviation between the actual value of the DC bus voltage and the rated value, while the output of reactive power is usually a set fixed value (usually zero);

[0016] The control relationship between the active power output of the AC / DC converter and the DC bus voltage is:

[0017] P n =k p (U dc -U dcn )+k i ∫(Udc -U dcn )dt (1)

[0018] Where P n is the active power reference value of the AC / DC converter, U dcn , U dc are the rated voltage and actual voltage of the DC bus at the AC / DC converter end, k p , k i They are the proportional time constant and integral time constant of PI control respectively.

[0019] As a further improvement of the technical solution, the overall control of the AC / DC converter is expressed as follows:

[0020]

[0021] Among them, V A Represents the grid-connected voltage of the AC / DC converter; P n , Q n , P A , Q A They are the active power reference value, reactive power reference value, actual active power, and actual reactive power of the AC / DC converter; k pp , k pi , k qp , k qi They are active proportional time constant, active integral time constant, reactive proportional time constant, and reactive integral time constant; U dcn , U dc are the rated voltage and actual voltage of the DC bus at the AC / DC converter end; k p , k i are the proportional time constant and integral time constant of PI control respectively; I d ,I q are the d-axis and q-axis components of the AC-side current of the AC / DC converter; is the grid-connected voltage phase of the AC / DC converter, U dk Indicates the DC bus capacitor voltage; P T represents the total power of the AC / DC converter; C represents the capacitance value of the DC bus; j represents the imaginary unit; It is the AC side current of the AC / DC converter.

[0022] As a further improvement of the technical solution, in step S2, the specific control strategy of the single-phase voltage frequency control is as follows:

[0023] The existence of the rotor inertia of the synchronous generator makes it have active frequency droop characteristics; the virtual synchronous machine characteristics of the DC / AC converter can have not only active frequency droop characteristics, but also reactive voltage droop characteristics;

[0024] The droop characteristic can be expressed by the following formula:

[0025] f-f0=-K a (P D -P0) (3)

[0026] V D -V0=-K b (Q D -Q0) (4)

[0027] Where f0 and V0 are the rated frequency and rated voltage of the DC / AC converter respectively; f, V D are the actual frequency and actual voltage of the DC / AC converter respectively; P0 and Q0 are the rated active power and rated reactive power of the DC / AC converter respectively; P D , Q D They are the actual active power and actual reactive power of the DC / AC converter respectively; K a , K b They are the active frequency droop coefficient and the reactive voltage droop coefficient respectively.

[0028] As a further improvement of the technical solution, the control principle analysis of the DC / AC converter includes:

[0029] The DC / AC converter is an inverter power supply; the active power output by the DC / AC converter is:

[0030]

[0031] In the formula, E, δ, X, and V represent the voltage amplitude, power angle, grid-connected reactance, and actual value of grid-connected voltage on the AC side of the inverter power supply, i.e., the DC / AC converter, respectively;

[0032] According to the above calculation, the active power P D Get the DC / AC converter frequency reference value fref:

[0033] fref-f0=-K a (P D -P0) (6)

[0034] Where f0 represents the rated frequency of the DC / AC converter; K a Indicates the active frequency droop coefficient;

[0035] The calculation formula of reactive power Q1 output by DC / AC converter is:

[0036]

[0037] In order to ensure that the reactive power Q1 output by the DC / AC converter does not exceed its allowable value, additional processing is performed for reactive power exceeding the range, specifically:

[0038]

[0039] Among them, uref2 is a reference value calculated to deal with the situation where the reactive power exceeds the upper limit; uref3 is a reference value calculated to deal with the situation where the reactive power exceeds the lower limit; Q_max and Q_min represent the maximum reactive power and minimum reactive power allowed to be output by the DC / AC converter respectively; k qmax It is a coefficient related to reactive power upper limit control, which is used to adjust the influence of reactive power on voltage reference value when it approaches the upper limit; k qmin is a coefficient related to reactive power lower limit control, and its effect is similar to k qmax Similar, but used to handle situations where reactive power is close to the lower limit; T qmax , T qmin They are the maximum power duration period and the minimum power duration period respectively;

[0040] Then, the preliminary inverter-type power supply grid-connected voltage reference value uref1 and the final inverter-type power supply grid-connected voltage reference value uref can be determined:

[0041] uref1-V0=-K b (Q D -Q0) (10)

[0042] Wherein, uref1 represents the preliminary reference value of the grid-connected voltage of the inverter power supply; V0 represents the rated voltage of the DC / AC converter; K b is the reactive voltage droop coefficient; Q D Indicates the actual reactive power of the DC / AC converter; Q0 indicates the rated reactive power of the DC / AC converter;

[0043] uref=uref1+uref2+uref3 (11)

[0044] Among them, uref is the final grid-connected voltage reference value of the inverter power supply;

[0045] The actual value of the grid-connected voltage of the DC / AC converter is:

[0046]

[0047] In the formula, Vlm represents the actual value of the grid-connected voltage of the DC / AC converter, Vlr represents the real part of the actual value of the grid-connected voltage of the DC / AC converter; Vli represents the imaginary part of the actual value of the grid-connected voltage of the DC / AC converter;

[0048] The deviation between the final grid-connected voltage reference value of the DC / AC converter and its actual grid-connected voltage value is obtained through PI control to obtain the PWM modulation amplitude Pm_in of the DC / AC converter, that is:

[0049] Pm_in=k p (uref-Vlm)+k i ∫(uref-Vlm)dt (13)

[0050] Among them, k p is the proportional time constant of PI control, k i is the integral time constant of PI control;

[0051] The PWM modulation phase dph iu of the DC / AC converter is calculated by the following formula:

[0052] dph iu=∫2π(fref-Fcom)dt (14)

[0053] Where Fcom is the rated frequency of the system.

[0054] As a further improvement of the technical solution, the voltage and frequency of the DC / AC converter are determined by its reactive voltage droop characteristics and active frequency droop characteristics and the action of the PI controller, and the droop control coefficient and the PI controller parameters determine its response characteristics;

[0055] Combining equations (5) to (14), the single-phase voltage-frequency control of the DC / AC converter can be expressed as follows:

[0056]

[0057] Among them, ω co is the system angular frequency; ω o represents the inertia of the power system, f0, V0, P0, Q0 are the rated frequency, rated grid-connected voltage, rated active power and rated reactive power of the DC / AC converter respectively; E, δ, f, X, V, V ref Respectively represent the AC side voltage amplitude, phase, frequency, grid-connected reactance, actual grid-connected voltage value and grid-connected voltage reference value of the DC / AC converter; P D , Q D They represent the actual active power and actual reactive power of the DC / AC converter respectively.

[0058] As a further improvement of the technical solution, in step S3, the specific control strategy of the single-phase source-grid-load-storage coordinated optimization control is as follows:

[0059] In the single-phase source-grid-load-storage coordinated optimization control, the objective function of minimizing the operating cost of photovoltaic, energy storage and DC / AC converter heavy overload control is expressed as follows:

[0060] minp=C pv (t)+C es (t)+C OL (t) (16)

[0061] In the formula, minp represents the goal of minimizing the operating cost, C pv (t) represents the operating cost of photovoltaic power generation during period t; C es (t) represents the operating cost of the energy storage system; C OL (t) represents the penalty cost of severe overload of the DC / AC converter.

[0062] As a further improvement of the technical solution, in the objective function of minimizing the operating cost, the calculation formulas for each part of the cost are as follows:

[0063] First, the operating costs of distributed photovoltaics: Distributed photovoltaics mainly consider the control costs of photovoltaic units, and the specific expression is as follows:

[0064]

[0065] Where N pv Indicates the number of photovoltaic units; λ p is the photovoltaic grid-connected electricity price; ΔP pv (t) represents the control power of unit p in time period t, unit: kW; δt is the duration of a time period, unit: hour;

[0066] Second, the operating cost of energy storage: The operating cost of energy storage includes the cost of energy storage charging and discharging. The specific expression is as follows:

[0067]

[0068] In the formula, l(t), l min , l max Respectively represent the time t value, daily minimum value, and daily maximum value of energy storage charging and discharging price, unit: yuan / kWh; Respectively represent the increased discharge power and charging power of unit e, unit: kW; N es Indicates the number of energy storage units;

[0069] Third, the penalty fee for heavy overload of DC / AC converter: The penalty fee for heavy overload of DC / AC converter reflects the tolerance for heavy overload of DC / AC converter, which is expressed by the penalty fee coefficient:

[0070]

[0071] In the formula, is the overload power of the DC / AC converter, l f is the penalty cost coefficient.

[0072] As a further improvement of the technical solution, the objective function of minimizing the operating cost should satisfy the following constraints:

[0073] 1) Photovoltaic constraints:

[0074]

[0075] In the formula, is the regulated active power of the i-th photovoltaic group at time t, which means the active power of the i-th photovoltaic group adjusted at time t relative to its initial operating state or the operating state at the previous moment; is the active power of the i-th photovoltaic group at the current time t, indicating the actual active power that the i-th photovoltaic group can output at the current time t; is the reactive power of the ith photovoltaic group at time t; S iN is the apparent power of the i-th inverter; is the maximum power angle of the ith photovoltaic group;

[0076] 2) Energy storage constraints include charge and discharge constraints and SOC constraints;

[0077] A. The charging and discharging power constraints are as follows:

[0078]

[0079] In the formula, They represent the maximum discharge power and maximum charging power of the energy storage unit respectively. Respectively represent the minimum discharge power and minimum charging power of the energy storage unit; They respectively represent the increased discharge power and charging power of the energy storage unit e at time t; They represent the discharge state and charge state of energy storage, respectively. They are both 0-1 variables. When the value is 1, it means discharge / charge, and when the value is 0, it means no discharge / no charge. The two are mutually exclusive, that is, they meet the following constraints:

[0080]

[0081] B. The calculation method of SOC constraint is:

[0082]

[0083] In the formula, represents the SOC of unit e in period t, represents the SOC of unit e at time t-1, Respectively represent the maximum and minimum allowable values ​​of SOC; It represents the charge and discharge power of unit e at time t, with charging being positive and discharging being negative; SOC(0) represents the initial capacity of SOC, and SOC(N) represents the SOC capacity of the last period;

[0084] 3) Power balance constraints:

[0085]

[0086] In the formula, is the active power of the i-th group of energy storage at the current time t; N ES is the number of energy storage; is the active power of the ith photovoltaic group at the current time t; N PV is the number of photovoltaic units; P Load (t) is the active power of the load at the current moment t; P i (t) is the active power of the DC / AC converter at the current moment t, and the overload power of the DC / AC converter The following constraints are met:

[0087]

[0088] In the formula, is the rated power of the DC / AC converter.

[0089] Compared with the prior art, the present invention has the following beneficial effects:

[0090] 1. This new low-voltage multi-port single-phase power supply equipment control method is based on the traditional low-voltage three-phase four-wire power supply technology. It uses power technology and equipment to achieve independent control of the power supply of phases A, B, and C in the three phases. While ensuring safe and reliable power supply for each phase, it can achieve multi-subject optimization among distributed photovoltaic, energy storage, and loads;

[0091] 2. In this new low-voltage multi-port single-phase power supply equipment control method, DC bus isolation can fundamentally solve the power quality problems such as three-phase imbalance, harmonics, voltage fluctuation and flicker in the low-voltage three-phase line, and has outstanding advantages in power quality management effect and management cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1This is a schematic diagram of an exemplary new low-voltage multi-port single-phase power supply in the present invention;

[0093] Figure 2 is an exemplary DC bus voltage-active power control block diagram in the present invention;

[0094] Figure 3 is a schematic diagram of an exemplary virtual synchronous machine control characteristic in the present invention;

[0095] Figure 4 FIG. 4 is a block diagram of an exemplary DC / AC converter virtual synchronous machine control in the present invention. DETAILED DESCRIPTION

[0096] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0097] Example 1

[0098] like Figure 1-Figure 4 As shown, this embodiment provides a novel low-voltage multi-port single-phase power supply device control method. First, a novel low-voltage single-phase multi-port power supply device consisting of an AC / DC converter, three DC / AC converters and a DC bus in the middle is constructed. An AC / DC converter is connected to and interacts with three DC / AC converters through the DC bus at the same time. Figure 1 The specific control method includes the following steps:

[0099] S1. DC bus voltage control: The DC bus voltage control of the new low-voltage multi-port single-phase power supply refers to the AC / DC converter adopting the Vdc-Q control mode, where Vdc is the DC bus voltage and Q is the total reactive power of the three-phase four-wire incoming line; the Vdc-Q control mode means that the AC / DC converter controls the DC bus voltage and the total reactive power of the three-phase four-wire incoming line at the same time;

[0100] In this step, the Vdc-Q control mode adjusts the active power of the AC / DC converter according to the deviation between the actual value and the rated value of the DC bus voltage, while the output of reactive power is usually a set fixed value (usually zero);

[0101] The control block diagram between the active power output of the AC / DC converter and the DC bus voltage is as follows: Figure 2 As shown, the control relationship between the active power output of the AC / DC converter and the DC bus voltage is:

[0102] P n=k p (U dc -U dcn )+k i ∫(U dc -U dcn )dt (1)

[0103] Where P n is the active power reference value of the AC / DC converter, U dcn , U dc are the rated voltage and actual voltage of the DC bus at the AC / DC converter end, k p , k i They are the proportional time constant and integral time constant of PI control respectively.

[0104] Figure 2 UDC stands for U dc , is the actual voltage of the DC bus at the AC / DC converter end; UDC_ref is the voltage reference value of the DC bus at the AC / DC converter end; dUDC means that the actual voltage of the DC bus at the AC / DC converter end is used as the input signal; Pmax and Pmin represent the maximum active power and the minimum active power respectively; Pref is P n , represents the active power reference value of the AC / DC converter; KDC and 1 / sTDC both represent the conversion elements in the AC / DC converter.

[0105] Therefore, the overall control of the AC / DC converter is expressed as follows:

[0106]

[0107] Among them, V A Represents the grid-connected voltage of the AC / DC converter. It reflects the actual voltage when the AC / DC converter is connected to the grid. It is an important monitoring and control basis in the entire control system. Its size will affect the energy exchange and power transmission characteristics between the converter and the grid. n , Q n , P A , Q A They are the active power reference value, reactive power reference value, actual active power, and actual reactive power of the AC / DC converter. n and Q n They are the active power reference value and reactive power reference value of the AC / DC converter. These two reference values ​​are the target values ​​set by the control system according to the desired operating state or external instructions, and are used to guide the converter to adjust its actual power output to achieve specific power supply requirements for the grid or load; for example, when maintaining the DC bus voltage stable or meeting specific power factor requirements, these reference values ​​will be set accordingly; PA and Q A They are the actual active power and actual reactive power of the AC / DC converter, which are the actual output power values ​​of the converter during operation obtained through actual measurement or calculation, reflecting the current working state of the converter and the actual power supply to the grid or load; the control system will make adjustments based on the deviation between the actual power and the reference power to make the actual power as close to the reference power as possible, thereby achieving stable power supply and optimized operation;

[0108] k pp , k pi , k qp , k qi They are active proportional time constant, active integral time constant, reactive proportional time constant, and reactive integral time constant; among them, k pp and k pi They are the active proportional time constant and the active integral time constant. In the AC / DC converter control system based on PI (proportional-integral) control, these two parameters determine the response characteristics of the active power control loop to the active power deviation; the proportional part (k pp ) immediately generates a control action according to the current active power deviation, and the integral part (k pi ) accumulates the active power deviation in the past period of time to eliminate the steady-state error so that the actual active power can accurately track the active power reference value; k qp and k qi They are the reactive proportional time constant and reactive integral time constant, which play similar roles in the reactive power control loop and determine the response speed and control accuracy of reactive power control to reactive power deviation. Reactive proportional control can quickly respond to changes in reactive power, while reactive integral control is used to eliminate the steady-state error of reactive power and ensure that reactive power output meets requirements, such as maintaining the power factor of the system within the expected range.

[0109] U dcn , U dc are the rated voltage and actual voltage of the DC bus at the AC / DC converter end; among them, U dcn It is the rated voltage of the DC bus at the AC / DC converter end. It is the standard voltage value that the DC bus should maintain when the system is designed. It is a fixed reference value used to measure whether the actual operating state of the DC bus voltage is normal. During the control process, the actual DC bus voltage U dc Will be with the rated voltage U dcn Compare the two and adjust the control strategy of the AC / DC converter according to the deviation to keep the DC bus voltage stable; U dcIt is the actual voltage of the DC bus at the AC / DC converter end. It is the voltage value of the DC bus obtained by real-time monitoring. Its value will be affected by many factors such as grid voltage fluctuation, load change and converter control action. The control system continuously monitors U dc , and with U dcn By comparison, the active power output of the converter is adjusted using methods such as PI control, thereby maintaining the DC bus voltage close to the rated value and ensuring the stable operation of the entire power supply system;

[0110] k p , k i are the proportional time constant and integral time constant of PI control respectively; I d ,I q It is the d-axis and q-axis components of the AC side current of the AC / DC converter; in the transformation of the three-phase stationary coordinate system to the two-phase rotating coordinate system (dq coordinate system) of the power system, decomposing the AC current into d-axis and q-axis components helps to simplify the analysis and control of the AC system. The d-axis current component is usually related to active power, while the q-axis current component is related to reactive power. By controlling I d and I q , can realize independent control of the active power and reactive power of AC / DC converter, so as to optimize the operating performance of the converter and meet various requirements of the power grid and load, such as realizing power factor correction, voltage regulation and other functions; is the grid-connected voltage phase of the AC / DC converter;

[0111] U dk Represents the DC bus capacitor voltage. In general power electronic converter circuits, capacitor voltage is an important state variable. It is related to energy storage and release, and will affect the dynamic response and stability of the system. T Indicates the total power of the AC / DC converter; C indicates the capacitance value of the DC bus. The DC bus capacitor plays the role of smoothing the DC voltage, storing energy and buffering power fluctuations in the system. The size of its capacitance value will affect the stability of the DC bus voltage, the dynamic response speed and the system's resistance to load changes and interference; the selection of appropriate capacitance value is crucial to ensure the reliable operation of the entire power supply system);

[0112] j represents the imaginary unit, which is used to represent the imaginary part of the phasor representation of complex electrical quantities (such as current, voltage, etc.) (in the analysis and calculation of AC circuits, especially when using the phasor method to describe sinusoidal steady-state circuits, the imaginary unit j plays a key role. It helps us include both amplitude and phase information in a complex expression, so as to facilitate circuit analysis and calculation). is the AC side current of the AC / DC converter, which is a comprehensive current variable, which may be expressed by the d-axis and q-axis current components (I d and I q ) synthesized AC side actual current; in power system analysis and control, AC side current is a key physical quantity, which reflects the energy exchange between the converter and the grid. Its size, phase and waveform quality are of great significance for evaluating the performance, stability and power quality of the system; the control system will The working state of the converter is adjusted through monitoring and analysis to achieve various control objectives, such as power factor correction, harmonic suppression, etc.

[0113] S2. Single-phase voltage and frequency control: The single-phase voltage and frequency control of the new low-voltage multi-port single-phase power supply refers to the DC / AC converter adopting the Vf virtual synchronous machine control mode, where V is the single-phase AC voltage output by the DC / AC converter, and f is its frequency; the Vf virtual synchronous machine control mode means that the DC / AC converter controls the single-phase AC voltage and frequency it outputs to ensure the power supply of the load connected to the phase line and the consumption of photovoltaic power;

[0114] In this step, the existence of the rotor inertia of the synchronous generator makes it have active frequency droop characteristics; the virtual synchronous machine characteristics of the DC / AC converter can not only have active frequency droop characteristics, but also have reactive voltage droop characteristics, such as Figure 3 As shown;

[0115] The droop characteristic can be expressed by the following formula:

[0116] f-f0=-K a (P D -P0) (3)

[0117] V D -V0=-K b (Q D -Q0) (4)

[0118] Where f0 and V0 are the rated frequency and rated voltage of the DC / AC converter respectively; f, V D They are the actual frequency and actual voltage of the DC / AC converter respectively; P0 and Q0 are the rated active power and rated reactive power of the DC / AC converter respectively; among them, P0 is the maximum active power that the converter can output under rated working conditions, which is an important performance indicator of the converter; in actual operation, the actual output active power of the converter will vary within a certain range according to the load demand and system control requirements, but usually should not exceed the rated active power to avoid overload damage to the converter; the rated active power plays an important reference role in system planning, equipment selection and operation control;

[0119] P D , Q D are the actual active power and actual reactive power of the DC / AC converter respectively; where P D It indicates the actual power size of the converter when it converts DC power into AC power and transmits it to the load or power grid. It is an important indicator to measure the converter's ability to provide useful power to the load. The size of active power directly affects the working state of the load and the energy conversion efficiency. In the power system, it needs to be accurately controlled to meet the power requirements of different loads and maintain the power balance of the system. Reactive power is used to describe the rate of energy exchange between energy storage elements such as inductors and capacitors and power sources in AC circuits, but it does not do work externally. Reactive power plays an important role in the power system, affecting the stability of voltage and the quality of power. Reasonable control of reactive power can achieve power factor correction, reduce the transmission loss of reactive current in the power grid, and improve the power supply efficiency and stability of the power grid. K a , K b They are the active frequency droop coefficient and the reactive voltage droop coefficient respectively.

[0120] Furthermore, the control principle analysis of a typical DC / AC converter includes: DC / AC converter is an inverter power supply; the active power output of the DC / AC converter is:

[0121]

[0122] In the formula, E, δ, X, and V represent the voltage amplitude, power angle, grid-connected reactance, and actual grid-connected voltage on the AC side of the inverter power supply, i.e., the DC / AC converter. Among them, E is the peak value of the AC voltage output by the inverter power supply, which determines the strength of the AC voltage, affects the ability of power transmission and the working voltage level of the load. In the power system, different loads and equipment may require specific voltage amplitudes to ensure normal operation, so the control of E is crucial to meet the load requirements. The δ power angle is an important parameter in the operation of the synchronous motor, which reflects the phase difference between the generator potential and the terminal voltage. In the virtual synchronous machine control of the DC / AC converter, the change of the power angle is closely related to the regulation of active power and reactive power. By controlling the power angle, the output power of the converter can be controlled, which is similar to the synchronous generator. The motor controls the output power by adjusting the rotor angle; the grid-connected reactance is the equivalent reactance faced by the inverter power supply when it is connected to the grid, including line reactance, transformer reactance, etc. The grid-connected reactance will affect the transmission characteristics of electric energy between the converter and the grid, such as the impact on the current size and phase, and then affect the distribution of active power and reactive power. In system analysis and control, it is necessary to consider the size of the grid-connected reactance to optimize the control strategy of the converter to improve the stability of the system and the power quality; the actual value of the grid-connected voltage is the actual grid voltage measured when the inverter power supply is connected to the grid. It is an external environmental parameter for the operation of the converter. The size and change of V will affect the output power, current, etc. of the converter. At the same time, the control of the converter also needs to be adjusted according to the actual situation of V to achieve good matching with the grid and stable operation.

[0123] According to the above calculation, the active power P D Get the DC / AC converter frequency reference value fref:

[0124] fref-f0=-K a (P D -P0) (6)

[0125] Among them, fref is the expected output frequency target value set by the control system for the converter, which is used to ensure that the frequency of the AC power output by the converter meets the grid standard or load requirements. In the power system, the stability of the frequency is crucial to ensure the normal operation of various electrical equipment. Therefore, it is necessary to use a control strategy to make the actual output frequency of the converter as close to the frequency reference value as possible. f0 represents the rated frequency of the DC / AC converter. It is the standard operating frequency specified when the converter is designed, which is usually consistent with the grid frequency (for example, 50Hz or 60Hz). The rated frequency is an important parameter for the normal operation of the converter. When analyzing and designing the control system, the rated frequency is used as a reference to evaluate and adjust the frequency characteristics of the converter to ensure that it can stably output AC power close to the rated frequency under different operating conditions; K aIt represents the active frequency droop coefficient, which is used to describe the frequency droop characteristics of the DC / AC converter when the active power changes. The droop coefficient determines the response relationship between active power and frequency. When the active power changes, the corresponding frequency adjustment can be calculated based on the droop coefficient. By reasonably setting K a , which can realize stable frequency control of the converter under different load conditions, and also facilitate power distribution and coordinated control between multiple converters when operating in parallel.

[0126] The calculation formula of reactive power Q1 output by DC / AC converter is:

[0127]

[0128] Q1 is the reactive power calculated based on the voltage amplitude E, power angle δ, grid voltage V and grid reactance X of the inverter power supply. It is used to evaluate the reactive power output of the converter in the current operating state in a specific control strategy or analysis, and provide a reference for subsequent reactive power control and adjustment.

[0129] In order to ensure that the reactive power Q1 output by the DC / AC converter does not exceed its allowable value, additional processing is performed for reactive power exceeding the range, specifically:

[0130]

[0131] Among them, uref2 is a reference value calculated to deal with the situation where reactive power exceeds the upper limit. When the calculated reactive power Q1 may exceed its maximum allowable value Ω_max, uref2 is calculated by formula (8) so that the voltage reference value can be adjusted in the subsequent control, thereby limiting the output of reactive power, preventing over-reactive power, protecting system equipment and maintaining power quality; uref3 is a reference value calculated to deal with the situation where reactive power exceeds the lower limit. When the reactive power Q1 may be lower than its minimum allowable value Q_min, uref3 is calculated by formula (9) and is also used to adjust the voltage reference value in the control to avoid under-reactive power, ensure that the system reactive power is within a reasonable range, and maintain the stable operation and power quality of the system;

[0132] Q_max and Q_min represent the maximum reactive power and minimum reactive power allowed to be output by the DC / AC converter, respectively; Q_max is the upper limit of reactive power determined based on system design requirements, equipment capacity, and grid operation specifications. Exceeding this value may cause problems such as increased system voltage, equipment overload, or deterioration of power quality. Therefore, during the control process, reactive power needs to be monitored and limited to ensure that it does not exceed Q_max; corresponding to Q_max, Q_min is the lower limit of reactive power. A value lower than this may affect the system's power factor, voltage stability and other performance indicators. Therefore, it is also necessary to constrain it in the control to ensure that reactive power fluctuates within a reasonable range and maintain the normal operation of the system; qmax It is a coefficient related to reactive power upper limit control, which is used to adjust the influence of reactive power on voltage reference value when it approaches the upper limit. qmax , the voltage reference value can be flexibly adjusted according to the actual situation of reactive power to achieve effective control of the reactive power upper limit, while avoiding excessive adjustment that may lead to system instability; k qmin is a coefficient related to reactive power lower limit control, and its effect is similar to k qmax Similar, but used to handle the situation where reactive power is close to the lower limit, k qmin The value of will affect the adjustment strategy of the voltage reference value when the reactive power is lower than the lower limit, thereby ensuring that the reactive power can be stabilized within a reasonable lower limit and maintain the normal operation of the system; T qmax , T qmin They are the maximum power duration period and the minimum power duration period respectively;

[0133] Then, the preliminary inverter-type power supply grid-connected voltage reference value uref1 and the final inverter-type power supply grid-connected voltage reference value uref can be determined:

[0134] uref1-V0=-K b (Q D -Q0) (10)

[0135] Among them, uref1 represents the preliminary inverter power grid-connected voltage reference value, which is based on the reactive power Q of the DC / AC converter. D With rated reactive power Q D The deviation of reactive voltage droop coefficient K b The target voltage value calculated is used to guide the voltage regulation of the DC / AC converter so that its output voltage is adjusted towards the reference value to meet the reactive voltage control requirements of the system; V0 represents the rated voltage of the DC / AC converter, which is the voltage value expected to be output by the converter under normal working conditions, and is used as a reference value for comparison and adjustment with the actual output voltage or reference voltage; K bis the reactive voltage droop coefficient, which determines the proportional relationship between reactive power change and voltage change and is used to achieve reactive voltage droop control. When the reactive power deviates from the rated value, the voltage adjustment is calculated based on this coefficient, so that the converter can automatically adjust the output voltage according to the reactive power demand of the load; Q D It indicates the actual reactive power of the DC / AC converter, reflecting the reactive power actually output by the converter in the current operating state. It changes with the load and is one of the important bases for controlling the voltage reference value. Q0 indicates the rated reactive power of the DC / AC converter, which is the reactive power value that should be output under rated working conditions specified when the converter is designed. It is used to compare with the actual reactive power, determine the deviation of the reactive power, and then adjust the voltage reference value.

[0136] uref=uref1+uref2+uref3 (11)

[0137] Among them, uref is the final grid-connected voltage reference value of the inverter power supply, which is the final target voltage reference value after comprehensive consideration of multiple factors. It is jointly determined by uref1, uref2 and uref3, and is used to control the PWM modulation of the DC / AC converter to achieve precise control of the output voltage;

[0138] like Figure 4 As shown in the figure, the "Pf Droop" module represents the active frequency droop characteristic, which is calculated based on the active power P calculated by the "PQ Cal" module. D The frequency reference value fref of the DC / AC converter is obtained; the "QV Droop" module represents the reactive voltage droop characteristic. However, in order to prevent the reactive power Q1 of the DC / AC converter from exceeding its allowable value, the module also adds processing for reactive power exceeding the range, namely formulas (8) and (9). Therefore, in addition to using the reactive power Q calculated by the "PQ Cal" module, the "QV Droop" module also uses the reactive power Q D In addition to determining the inverter-type power grid-connected voltage reference value uref1, the outputs uref2 and uref3 of formulas (8) and (9) must also be considered. Their sum is the final inverter-type power grid-connected voltage reference value uref; Figure 4 Inr and Ini represent the real and imaginary components of the current, respectively; Vnr and Vni represent the real and imaginary components of the voltage, respectively; du represents the error signal, and Pm_in represents the PI regulation signal input to the inverter.

[0139] Figure 4 Where Vlm is the actual value of the grid-connected voltage of the DC / AC converter, that is:

[0140]

[0141] Wherein, Vlm represents the actual value of the grid-connected voltage of the DC / AC converter, Vlr represents the real part of the actual value of the grid-connected voltage of the DC / AC converter, and in the complex number representation, it is used to represent the component of the voltage on the real axis, and together with the imaginary part Vli, it constitutes a complete complex representation of the actual value of the grid-connected voltage. In this way, some power system analysis and control calculations involving complex number operations can be more conveniently performed; Vli represents the imaginary part of the actual value of the grid-connected voltage of the DC / AC converter, and together with the real part Vlr, it completely describes the complex form of the grid-connected voltage. The existence of the imaginary part reflects the phase information of the voltage in the power system, which is of great significance for analyzing and controlling power phenomena involving phase relationships (such as reactive power, power factor, etc.).

[0142] The deviation between the final grid-connected voltage reference value of the DC / AC converter and its actual grid-connected voltage value is obtained through PI control to obtain the PWM modulation amplitude Pm_in of the DC / AC converter, that is:

[0143] Pm_in=k p (uref-Vlm)+k i ∫(uref-Vlm)dt (13)

[0144] Among them, Pm_in represents the PWM modulation amplitude of the DC / AC converter, which determines the amplitude of the PWM signal, and then controls the on and off time of the power switch device in the DC / AC converter to achieve control of the output voltage and current. By adjusting Pm_in, the voltage and frequency output by the converter can meet the system requirements and achieve stable power supply to the load; p is the proportional time constant of PI control, k i is the integral time constant of PI control;

[0145] The PWM modulation phase dphiu of the DC / AC converter is calculated by the following formula:

[0146] dph iu=∫2π(fref-Fcom)dt (14)

[0147] Where Fcom is the rated frequency of the system; dph iu represents the PWM modulation phase of the DC / AC converter, which determines the phase change of the PWM signal and is crucial for controlling the phase and frequency of the output voltage of the DC / AC converter. By adjusting dph iu, the voltage output by the converter can be synchronized with the grid voltage or other reference signals, and stable control of the phase and frequency can be achieved to ensure the normal operation of the power system. For example, when connected to the grid, the phase and frequency of the converter output voltage need to be strictly matched with the grid voltage to achieve efficient and stable power transmission and power exchange. The specific calculation method may involve the rated frequency of the system Fcom and other parameters related to frequency control. By reasonably designing the calculation method of dph, the output frequency of the DC / AC converter can be accurately controlled to meet the frequency requirements in different application scenarios, such as the standard grid frequency of 50Hz or 60Hz, or flexibly adjusted according to actual needs in special applications such as microgrids.

[0148] Depend on Figure 4 As can be seen from the above analysis, the voltage and frequency of the DC / AC converter are determined by its reactive voltage droop characteristics and active frequency droop characteristics as well as the action of the PI controller. The droop control coefficient and PI controller parameters determine its response characteristics.

[0149] Combining equations (5) to (14), the single-phase voltage-frequency control of the DC / AC converter can be expressed as follows:

[0150]

[0151] Among them, ω co is the system angular frequency, which is a basic frequency parameter of the entire power system operation and is related to the synchronous operation and stability of the system. The rate of change of the power angle δ is used to calculate the power angle, which reflects the influence of the relationship between the system frequency and the actual frequency f of the converter on the power angle change; ω o It represents the inertia (or other dynamic characteristics) of the power system, plays a role in adjusting the relationship between the power angle change rate and the frequency difference, and helps to make reasonable dynamic adjustments to the power angle in the control system;

[0152] f0, V0, P0, Q0 are the rated frequency, rated grid-connected voltage, rated active power and rated reactive power of the DC / AC converter respectively; E, δ, f, X, V, V ref Respectively represent the AC side voltage amplitude, phase, frequency, grid-connected reactance, actual grid-connected voltage value and grid-connected voltage reference value of the DC / AC converter; P D , Q D They represent the actual active power and actual reactive power of the DC / AC converter respectively.

[0153] S3. Single-phase source-grid-load-storage coordinated optimization control: The single-phase source-grid-load-storage coordinated optimization control of the new low-voltage multi-port single-phase power supply refers to the coordinated optimization control between the DC / AC converter and the distributed photovoltaic and energy storage connected to the single-phase line it supplies power. Its goal is to ensure that the DC / AC converter is not overloaded and to maximize the benefits of multiple distributed photovoltaic and energy storage entities.

[0154] In this step, the objective function of minimizing the operating cost of photovoltaic, energy storage and DC / AC converter heavy overload control in the single-phase source-grid-load-storage coordinated optimization control is expressed as follows:

[0155] minp=C pv (t)+C es (t)+C OL (t) (16)

[0156] In the formula, minp represents the goal of minimizing the operating cost, C pv (t) represents the operating cost of photovoltaic power generation during period t; C es (t) represents the operating cost of the energy storage system; C OL (t) represents the penalty cost of severe overload of the DC / AC converter.

[0157] Specifically, the calculation formula for each part of the cost is as follows:

[0158] First, the operating costs of distributed photovoltaics: Distributed photovoltaics mainly consider the control costs of photovoltaic units, and the specific expression is as follows:

[0159]

[0160] Where N pv Indicates the number of photovoltaic units; λ p is the photovoltaic grid-connected electricity price; ΔP pv (t) represents the control power of unit p in time period t, unit: kW; δt is the duration of a time period, unit: hour;

[0161] Second, the operating cost of energy storage: The operating cost of energy storage includes the cost of energy storage charging and discharging. The specific expression is as follows:

[0162]

[0163] In the formula, l(t), l min , l max Respectively represent the time t value, daily minimum value, and daily maximum value of energy storage charging and discharging price, unit: yuan / kWh; Respectively represent the increased discharge power and charging power of unit e, unit: kW; N es Indicates the number of energy storage units;

[0164] Third, the penalty fee for heavy overload of DC / AC converter: The penalty fee for heavy overload of DC / AC converter reflects the tolerance for heavy overload of DC / AC converter, which is expressed by the penalty fee coefficient:

[0165]

[0166] In the formula, is the overload power of the DC / AC converter, l f is the penalty cost coefficient.

[0167] Furthermore, the objective function of minimizing the running cost should satisfy the following constraints:

[0168] 1) Photovoltaic constraints:

[0169]

[0170] In the formula, is the regulated active power of the i-th photovoltaic group at time t, which means the active power of the i-th photovoltaic group adjusted at time t relative to its initial operating state or the operating state at the previous moment; is the active power of the i-th photovoltaic group at the current time t, indicating the actual active power that the i-th photovoltaic group can output at the current time t; is the reactive power of the ith photovoltaic group at time t; S iN is the apparent power of the i-th inverter; is the maximum power angle of the ith photovoltaic group;

[0171] 2) Energy storage constraints include charge and discharge constraints and SOC constraints;

[0172] A. The charging and discharging power constraints are as follows:

[0173]

[0174] In the formula, They represent the maximum discharge power and maximum charging power of the energy storage unit respectively. They represent the minimum discharge power and minimum charging power of the energy storage unit respectively; the energy storage can be operated in the optimal charging power state by setting the maximum charging power and the minimum charging power; They respectively represent the increased discharge power and charging power of the energy storage unit e at time t; They represent the discharge state and charge state of energy storage, respectively. They are both 0-1 variables. When the value is 1, it means discharge / charge, and when the value is 0, it means no discharge / no charge. The two are mutually exclusive, that is, they meet the following constraints:

[0175]

[0176] B. The calculation method of SOC constraint is:

[0177]

[0178] In the formula, represents the SOC of unit e in period t, represents the SOC of unit e at time t-1, Respectively represent the maximum and minimum allowable values ​​of SOC; It represents the charge and discharge power of unit e at time t, with charging being positive and discharging being negative; SOC(0) represents the initial capacity of SOC, and SOC(N) represents the SOC capacity of the last period;

[0179] 3) Power balance constraints:

[0180]

[0181] In the formula, is the active power of the i-th group of energy storage at the current time t; N ES is the number of energy storage; is the active power of the ith photovoltaic group at the current time t; N PV is the number of photovoltaic units; P Lpad (t) is the active power of the load at the current moment t; P i (t) is the active power of the DC / AC converter at the current moment t, and the overload power of the DC / AC converter The following constraints are met:

[0182]

[0183] In the formula, is the rated power of the DC / AC converter.

[0184] In summary, this embodiment proposes a new power supply technology and equipment for low-voltage power grids. Through power electronic switching devices and flexible and fast control technology, it realizes functions such as three-phase unbalance control, harmonic control, voltage fluctuation and flicker control, voltage reactive power control, and source-grid-load-storage coordinated optimization. It aims to comprehensively solve power quality problems such as high / low voltage, three-phase unbalance, voltage fluctuation and flicker, and harmonics, and has outstanding advantages in power quality control effect and control cost.

[0185] Those skilled in the art will appreciate that the process of implementing all or part of the steps of the above embodiments may be completed by hardware, or may be completed by instructing related hardware through a program.

[0186] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A novel low-voltage multi-port single-phase power supply equipment control method, characterized in that: First, a novel low-voltage single-phase multi-port power supply device consisting of an AC / DC converter, three DC / AC converters and a DC bus in the middle is constructed; the control method includes the following steps: S1. DC bus voltage control: The DC bus voltage control of the new low-voltage multi-port single-phase power supply refers to the AC / DC converter adopting the Vdc-Q control mode, where Vdc is the DC bus voltage and Q is the total reactive power of the three-phase four-wire incoming line; the Vdc-Q control mode means that the AC / DC converter controls the DC bus voltage and the total reactive power of the three-phase four-wire incoming line at the same time; S2. Single-phase voltage and frequency control: The single-phase voltage and frequency control of the new low-voltage multi-port single-phase power supply refers to the DC / AC converter adopting the Vf virtual synchronous machine control mode, where V is the single-phase AC voltage output by the DC / AC converter, and f is its frequency; the Vf virtual synchronous machine control mode means that the DC / AC converter controls the single-phase AC voltage and frequency it outputs to ensure the power supply of the load connected to the phase line and the consumption of photovoltaic power; S3. Single-phase source, grid, load and storage coordinated optimization control: The single-phase source, grid, load and storage coordinated optimization control of the new low-voltage multi-port single-phase power supply refers to the coordinated optimization control between the DC / AC converter and the distributed photovoltaic and energy storage connected to the single-phase line it supplies power.

2. According to claim 1, the novel low-voltage multi-port single-phase power supply equipment control method is characterized in that: In the novel low-voltage single-phase multi-port power supply device, one AC / DC converter is connected and exchanges energy with three DC / AC converters via a DC bus.

3. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 1 is characterized in that: In step S1, the specific control strategy of the DC bus voltage control is as follows: The Vdc-Q control mode adjusts the active power of the AC / DC converter according to the deviation between the actual value of the DC bus voltage and the rated value, while the output of reactive power is usually a set fixed value; The control relationship between the active power output of the AC / DC converter and the DC bus voltage is: P n =k p (YOU ac -YOU dcn )+k i ∫(You dc -YOU dcn )dt (1) Where P n is the active power reference value of the AC / DC converter, U dcn , U dc are the rated voltage and actual voltage of the DC bus at the AC / DC converter end, k p , k i They are the proportional time constant and integral time constant of PI control respectively.

4. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 3 is characterized in that: The overall control of the AC / DC converter is expressed as follows: Among them, V A Represents the grid-connected voltage of the AC / DC converter; P n , Q n , P A , Q A They are the active power reference value, reactive power reference value, actual active power, and actual reactive power of the AC / DC converter; k pp , k pi , k qp , k qi They are active proportional time constant, active integral time constant, reactive proportional time constant, and reactive integral time constant; U dcn , U dc are the rated voltage and actual voltage of the DC bus at the AC / DC converter end; k p , k i are the proportional time constant and integral time constant of PI control respectively; I d ,I q are the d-axis and q-axis components of the AC-side current of the AC / DC converter; is the grid-connected voltage phase of the AC / DC converter, U dk Indicates the DC bus capacitor voltage; P T Indicates the total power of the AC / DC converter; C indicates the capacitance value of the DC bus; j indicates an imaginary unit, which is used to indicate electrical quantities in complex form; It is the AC side current of the AC / DC converter.

5. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 1 is characterized in that: In step S2, the specific control strategy of single-phase voltage frequency control is as follows: The existence of the rotor inertia of the synchronous generator makes it have active frequency droop characteristics; the virtual synchronous machine characteristics of the DC / AC converter can have not only active frequency droop characteristics, but also reactive voltage droop characteristics; The droop characteristic can be expressed by the following formula: f-f0=-K a (P D -P0) (3) V D -V0=-K b (Q D -Q0) (4) Where f0 and V0 are the rated frequency and rated voltage of the DC / AC converter respectively; f, V D are the actual frequency and actual voltage of the DC / AC converter respectively; P0 and Q0 are the rated active power and rated reactive power of the DC / AC converter respectively; P D , Q D They are the actual active power and actual reactive power of the DC / AC converter respectively; K a , K b They are the active frequency droop coefficient and the reactive voltage droop coefficient respectively.

6. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 5 is characterized in that: The control principle analysis of the DC / AC converter includes: The DC / AC converter is an inverter power supply; the active power output by the DC / AC converter is: In the formula, E, δ, X, and V represent the voltage amplitude, power angle, grid-connected reactance, and actual value of grid-connected voltage on the AC side of the inverter power supply, i.e., the DC / AC converter, respectively; According to the above calculation, the active power P D Get the DC / AC converter frequency reference value fref: fref-f0=-K a (P D -P0) (6) Where f0 represents the rated frequency of the DC / AC converter; K a Indicates the active frequency droop coefficient; The calculation formula of reactive power Q1 output by DC / AC converter is: In order to ensure that the reactive power Q1 output by the DC / AC converter does not exceed its allowable value, additional processing is performed for reactive power exceeding the range, specifically: Among them, uref2 is a reference value calculated to deal with the situation where the reactive power exceeds the upper limit; uref3 is a reference value calculated to deal with the situation where the reactive power exceeds the lower limit; Q_max and Q_min represent the maximum reactive power and minimum reactive power allowed to be output by the DC / AC converter respectively; k qmax It is a coefficient related to reactive power upper limit control, which is used to adjust the influence of reactive power on voltage reference value when it approaches the upper limit; k qmin is a coefficient related to reactive power lower limit control, and its effect is similar to k qmax Similar, but used to handle situations where reactive power is close to the lower limit; T qmax , T qmin They are the maximum power duration period and the minimum power duration period respectively; Then, the preliminary inverter-type power supply grid-connected voltage reference value uref1 and the final inverter-type power supply grid-connected voltage reference value uref can be determined: uref1-V0=-K b (Q D -Q0) (10) Wherein, uref1 represents the preliminary reference value of the grid-connected voltage of the inverter power supply; V0 represents the rated voltage of the DC / AC converter; K b is the reactive voltage droop coefficient; Q D Indicates the actual reactive power of the DC / AC converter; Q0 indicates the rated reactive power of the DC / AC converter; uref=uref1+uref2+uref3 (11) Among them, uref is the final grid-connected voltage reference value of the inverter power supply; The actual value of the grid-connected voltage of the DC / AC converter is: Wherein, Vlm represents the actual value of the grid-connected voltage of the DC / AC converter, Vlr represents the real part of the actual value of the grid-connected voltage of the DC / AC converter, and Vli represents the imaginary part of the actual value of the grid-connected voltage of the DC / AC converter; The deviation between the final grid-connected voltage reference value of the DC / AC converter and its actual grid-connected voltage value is obtained through PI control to obtain the PWM modulation amplitude Pm_in of the DC / AC converter, that is: Pm_in=k p (uref-Vlm)+k i ∫(uref-Vlm)dt (13) Among them, k p is the proportional time constant of PI control, k i is the integral time constant of PI control; The PWM modulation phase dph iu of the DC / AC converter is calculated by the following formula: dph iu=∫2π(fref-Fcom)dt (14) Where Fcom is the rated frequency of the system.

7. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 6 is characterized in that: The voltage and frequency of the DC / AC converter are determined by its reactive voltage droop characteristics and active frequency droop characteristics and the action of the PI controller, and the droop control coefficient and the PI controller parameters determine its response characteristics; Combining equations (5) to (14), the single-phase voltage-frequency control of the DC / AC converter can be expressed as follows: Among them, ω co is the system angular frequency; ω o represents the inertia of the power system, f0, V0, P0, Q0 are the rated frequency, rated grid-connected voltage, rated active power and rated reactive power of the DC / AC converter respectively; E, δ, f, X, V, V ref Respectively represent the AC side voltage amplitude, phase, frequency, grid-connected reactance, actual grid-connected voltage value and grid-connected voltage reference value of the DC / AC converter; P D , Q D They represent the actual active power and actual reactive power of the DC / AC converter respectively.

8. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 1 is characterized in that: In step S3, the specific control strategy for the coordinated optimization control of the single-phase source, grid, load and storage is as follows: In the single-phase source-grid-load-storage coordinated optimization control, the objective function of minimizing the operating cost of photovoltaic, energy storage and DC / AC converter heavy overload control is expressed as follows: minp=C pv (t)+C es (t)+C OL (t) (16) In the formula, minp represents the goal of minimizing the operating cost, C pv (t) represents the operating cost of photovoltaic power generation during period t; C es (t) represents the operating cost of the energy storage system; C OL (t) represents the penalty cost of severe overload of the DC / AC converter.

9. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 8 is characterized in that: In the objective function of minimizing the operating cost, the calculation formulas for each part of the cost are as follows: First, the operating costs of distributed photovoltaics: Distributed photovoltaics mainly consider the control costs of photovoltaic units, and the specific expression is as follows: Where N pv Indicates the number of photovoltaic units; λ p is the photovoltaic grid-connected electricity price; ΔP pv (t) represents the control power of unit p in period t, unit: kW; δt is the duration of a time period, unit: hour; Second, the operating cost of energy storage: The operating cost of energy storage includes the cost of energy storage charging and discharging. The specific expression is as follows: In the formula, l(t), l min , l max Respectively represent the time t value, daily minimum value, and daily maximum value of energy storage charging and discharging price, unit: yuan / kWh; Respectively represent the increased discharge power and charging power of unit e, unit: kW; N es Indicates the number of energy storage units; Third, the penalty fee for heavy overload of DC / AC converter: The penalty fee for heavy overload of DC / AC converter reflects the tolerance for heavy overload of DC / AC converter, which is expressed by the penalty fee coefficient: In the formula, is the overload power of the DC / AC converter, l f is the penalty cost coefficient.

10. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 9 is characterized in that: The objective function of minimizing the operating cost should satisfy the following constraints: 1) Photovoltaic constraints: In the formula, is the regulated active power of the i-th photovoltaic group at time t, which means the active power of the i-th photovoltaic group adjusted at time t relative to its initial operating state or the operating state at the previous moment; is the active power of the i-th photovoltaic group at the current time t, indicating the actual active power that the i-th photovoltaic group can output at the current time t; is the reactive power of the ith photovoltaic group at time t; S iN is the apparent power of the i-th inverter; is the maximum power angle of the ith photovoltaic group; 2) Energy storage constraints include charge and discharge constraints and SOC constraints; A. The charging and discharging power constraints are as follows: In the formula, They represent the maximum discharge power and maximum charging power of the energy storage unit respectively. Respectively represent the minimum discharge power and minimum charging power of the energy storage unit; They respectively represent the increased discharge power and charging power of the energy storage unit e at time t; They represent the discharge state and charge state of energy storage, respectively. They are both 0-1 variables. When the value is 1, it means discharge / charge, and when the value is 0, it means no discharge / no charge. The two are mutually exclusive, that is, they meet the following constraints: B. The calculation method of SOC constraint is: In the formula, represents the SOC of unit e in period t, represents the SOC of unit e at time t-1, Respectively represent the maximum and minimum allowable values ​​of SOC; It represents the charge and discharge power of unit e at time t, with charging being positive and discharging being negative; SOC(0) represents the initial capacity of SOC, and SOC(N) represents the SOC capacity of the last period; 3) Power balance constraints: In the formula, is the active power of the i-th group of energy storage at the current time t; N ES is the number of energy storage; is the active power of the ith photovoltaic group at the current time t; N PV is the number of photovoltaic units; P Load (t) is the active power of the load at the current moment t; P i (t) is the active power of the DC / AC converter at the current moment t, and the overload power of the DC / AC converter The following constraints are met: In the formula, is the rated power of the DC / AC converter.

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