A novel control method for low-voltage multi-port single-phase power supply equipment

Abstract

The present invention relates to the field of distribution network management technology, and specifically to a novel low-voltage multi-port single-phase power supply equipment control method. The method comprises: constructing 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; firstly, adopting a Vdc-Q control mode to control the DC bus voltage, secondly adopting a Vf virtual synchronous machine control mode to control the single-phase voltage and frequency, and finally performing single-phase source-grid-load-storage coordinated optimization control. The present invention is designed to achieve independent control of the power supply of each phase A, B, and C in the three phases through power technology and equipment. While ensuring safe and reliable power supply of each phase, it can achieve multi-subject optimization among distributed photovoltaic, energy storage, and loads; through DC bus isolation, it can fundamentally solve the power quality problems such as three-phase imbalance, harmonics, voltage fluctuation and flicker of the low-voltage three-phase line, and has outstanding advantages in terms of power 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 clean energy, 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 fluctuation and flicker, and harmonics are more prominent, seriously affecting the safe and high-quality power supply of low-voltage distribution networks.

[0003] Traditionally, high / low voltage issues are addressed using on-load tap-changing transformers and reactive power compensation. Three-phase imbalance is addressed by using phase-changing switches to change the load phase, thereby improving the three-phase imbalance. Voltage fluctuations, flicker, and harmonics are addressed primarily through active power filters and dynamic voltage restorers. However, these methods still have technical deficiencies, such as:

[0004] First, to address high / low voltage issues, on-load tap-changing transformers and reactive power compensation have traditionally been used. However, both these methods offer discrete regulation, not continuous adjustment. Furthermore, the number of adjustments required affects the lifespan of the equipment.

[0005] Secondly, to address the three-phase imbalance problem, phase-changing switches are mainly used to change the load connection phase to improve the three-phase imbalance. However, phase-changing switches can only partially solve the three-phase imbalance problem, not completely, and there are risks such as phase short circuits and short-term power outages.

[0006] Third, problems such as voltage fluctuations, 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] Generally speaking, traditional methods offer single solutions to single problems, and their effectiveness remains unsatisfactory, with shortcomings in technical performance, cost, and lifespan. To address this issue, we propose a novel control method for low-voltage, multi-port, single-phase power supply equipment to address the issue of safe, high-quality power supply in low-voltage distribution networks, particularly the power quality issues such as high / low voltage, three-phase imbalance, voltage fluctuation and flicker, and harmonics that arise when a large number of distributed photovoltaic systems are connected to the low-voltage distribution network. Summary of the Invention

[0008] The object 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] To solve the above technical problems, the present invention 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 is constructed, which is composed of an AC / DC converter, three DC / AC converters, and a DC bus in the middle. The control method includes 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 its output single-phase AC voltage and frequency to ensure the power supply of the load connected to the phase line and the absorption 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 present technical solution, in the novel low-voltage single-phase multi-port power supply device, one AC / DC converter is simultaneously connected and exchanges energy with three DC / AC converters via a DC bus.

[0014] As a further improvement of the present technical solution, in step S1, the specific control strategy for 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 They 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 this 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 present technical solution, in step S2, the specific control strategy of the single-phase voltage-frequency control is as follows:

[0023] The existence of rotor inertia of synchronous generator makes it have active frequency droop characteristics. The virtual synchronous machine characteristics of 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 this 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] Where 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, 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 for the reactive power Q1 output by the 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 added to deal with the reactive power exceeding the range, specifically as follows:

[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 and minimum reactive power values ​​allowed to be output by the DC / AC converter respectively; k qmax k 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; qmin It 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 grid-connected voltage reference value 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 inverter power grid-connected voltage reference value;

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

[0046]

[0047] Where 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 DC / AC converter PWM modulation amplitude Pm_in, 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 present 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. 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, and 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 Represent the actual active power and actual reactive power of the DC / AC converter respectively.

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

[0059] In the single-phase source-grid-load-storage coordinated optimization control, the objective function for 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] Where 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 this 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, which can be expressed 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 costs of energy storage: The operating costs of energy storage include the cost of energy storage charging and discharging. The specific expression is as follows:

[0067]

[0068] Where, 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 severe overload of DC / AC converter: The penalty fee for severe overload of DC / AC converter reflects the tolerance level for severe overload of DC / AC converter, which is expressed by the penalty fee coefficient:

[0070]

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

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

[0073] 1) Photovoltaic constraints:

[0074]

[0075] Where, 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 ith photovoltaic group at the current time t, indicating the actual active power that the ith photovoltaic group can output at the current time t; is the reactive power of the PV group i 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 charge and discharge power constraints are as follows:

[0078]

[0079] Where, Respectively represent the maximum discharge power and maximum charging power of the energy storage unit, Respectively represent the minimum discharge power and minimum charging power of the energy storage unit; They represent the increased discharge power and charging power of the energy storage unit e at time t respectively; Respectively represent the discharge state and charge state of energy storage, both are 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] Where, represents the SOC of unit e during 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] Where, 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 units; is the active power of the PV group i 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] Where, 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 builds on traditional low-voltage, three-phase, four-wire power supply technology by using power technology and equipment to achieve independent control of the power supply for phases A, B, and C. This ensures safe and reliable power supply for each phase while enabling multi-agent optimization among distributed photovoltaics, 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 power quality problems such as three-phase imbalance, harmonics, voltage fluctuation and flicker in low-voltage three-phase lines, 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 This is an exemplary DC bus voltage-active power control block diagram of 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 This is an exemplary DC / AC converter virtual synchronous machine control block diagram in the present invention. DETAILED DESCRIPTION

[0096] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall 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 exchanges energy with the three DC / AC converters through the DC bus. 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 of the DC bus voltage and the rated value, 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 They 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 In the UDC, 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 value 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 respectively; among them, P n and Q n These are the active power reference value and reactive power reference value of the AC / DC converter. These two reference values ​​are target values ​​set by the control system according to the desired operating state or external instructions. They 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 DC bus voltage stability or meeting specific power factor requirements, these reference values ​​will be set accordingly.A and Q A The actual active power and actual reactive power of the AC / DC converter are measured or calculated as the actual output power of the converter during operation. They reflect the converter's current operating status and the actual power supply to the grid or load. The control system adjusts the actual power according to the deviation between the actual power and the reference power to ensure that the actual power is 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, respectively. 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 These are the reactive proportional time constant and the 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 deviations. Reactive proportional control can quickly respond to changes in reactive power, while reactive integral control is used to eliminate steady-state errors in reactive power and ensure that reactive power output meets requirements, such as maintaining the system power factor within the desired 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 status of the DC bus voltage is normal. During the control process, the actual DC bus voltage U dc Will be with 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, PI control and other methods are used to adjust the active power output of the converter, 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 from 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 the active power, while the q-axis current component is related to the reactive power. By controlling I d and I q , can realize independent control of the active power and reactive power of AC / DC converter, thereby optimizing the operating performance of the converter and meeting 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 affects the dynamic response and stability of the system. T =(C) represents the total power of the AC / DC converter; C represents the capacitance of the DC bus. The DC bus capacitor smoothes the DC voltage, stores energy, and buffers power fluctuations in the system. Its capacitance affects the stability of the DC bus voltage, its dynamic response speed, and the system's resistance to load changes and interference. Choosing the right capacitance value is crucial to ensuring 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, making circuit analysis and calculation more convenient). is the AC side current of the AC / DC converter, which is a comprehensive current variable, which may be obtained through 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 monitoring and analysis are used to adjust the working state of the converter to achieve various control goals, such as power factor correction and harmonic suppression.

[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 its output single-phase AC voltage and frequency to ensure the power supply of the load connected to the phase line and the absorption 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 have not only active frequency droop characteristics, but also 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 are the actual frequency and actual voltage of the DC / AC converter, respectively; P0 and Q0 are the rated active and rated reactive power of the DC / AC converter, respectively; P0 is the maximum active power that the converter can output under rated operating conditions and 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 based on load demand and system control requirements, but generally should not exceed the rated active power to avoid converter overload damage; 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; among them, P D Active power refers to the actual power of a converter that converts DC power into AC power and transmits it to the load or grid. It is an important indicator for measuring the converter's ability to provide useful power to the load. Active power directly affects the load's operating state and energy conversion efficiency. In the power system, it needs to be precisely controlled to meet the power requirements of different loads and maintain the system's power balance. Reactive power is used to describe the rate of energy exchange between energy storage elements such as inductors and capacitors and the power supply in an AC circuit, but does not perform external work. Reactive power plays an important role in the power system, affecting voltage stability and power quality. Reasonable control of reactive power can achieve power factor correction, reduce transmission losses of reactive current in the power grid, and improve the power supply efficiency and stability of the grid. 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: a DC / AC converter is an inverter-type 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 value of 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 to transmit power 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 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 its 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 thus affect the distribution of active power and reactive power. In system analysis and control, the size of the grid-connected reactance needs to be considered to optimize the control strategy of the converter to improve the stability and power quality of the system; the actual value of the grid voltage is the actual measured grid voltage when the inverter power supply is connected to the grid. It is the external environmental parameter of the converter operation. 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 standards or load requirements. In the power system, frequency stability 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 and 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 benchmark 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 achieve stable frequency control of the converter under different load conditions, and also facilitate power distribution and coordinated control between multiple converters when running in parallel.

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

[0127]

[0128] Q1 is the reactive power calculated based on parameters such as 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 under 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 added to deal with the reactive power exceeding the range, specifically as follows:

[0130]

[0131] Among them, uref2 is a reference value calculated to deal with the situation where the 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 excessive reactive power, protecting system equipment and maintaining power quality; uref3 is a reference value calculated to deal with the situation where the 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 insufficient 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 and minimum reactive power outputs allowed 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 lead to 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 cause system instability; k qmin It is a coefficient related to reactive power lower limit control, and its effect is similar to k qmax Similar, but used to deal with 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 grid-connected voltage reference value of the inverter power supply, which is based on the reactive power Q of the DC / AC converter. D and rated reactive power Q D The deviation of reactive voltage droop coefficient K b The calculated target voltage value 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 expected output voltage value of the converter under normal working conditions. It is used as a reference value for comparison and adjustment with the actual output voltage or reference voltage. K bThe reactive voltage droop coefficient determines the proportional relationship between reactive power change and voltage change and is used to implement reactive voltage droop control. When the reactive power deviates from the rated value, the voltage adjustment is calculated based on this coefficient, allowing the converter to automatically adjust the output voltage according to the reactive power demand of the load. D It represents 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 represents the rated reactive power of the DC / AC converter, which is the reactive power value that should be output under rated operating conditions specified during converter design. It is used to compare with the actual reactive power to determine the deviation of the reactive power and adjust the voltage reference value.

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

[0137] Among them, uref is the final inverter power grid-connected voltage reference value, which is the final target voltage reference value after comprehensive consideration of multiple factors. It is 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 a 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 grid-connected voltage reference value uref1 of the inverter power supply, the outputs uref2 and uref3 of formulas (8) and (9) must also be considered. Their sum is the final grid-connected voltage reference value uref of the inverter power supply; 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] Where Vlm represents the actual value of the DC / AC converter's grid-connected voltage, and Vlr represents the real part of the actual value of the DC / AC converter's grid-connected voltage. In complex number representation, it is used to represent the voltage component on the real axis, and together with the imaginary part Vli, it constitutes the complete complex representation of the actual value of the grid-connected voltage. This method makes it easier to perform some power system analysis and control calculations involving complex number operations. Vli represents the imaginary part of the actual value of the DC / AC converter's grid-connected voltage, and together with the real part Vlr, it completely describes the complex form of the grid 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 and power factor).

[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 DC / AC converter PWM modulation amplitude Pm_in, 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 switching devices in the DC / AC converter to achieve control of the output voltage and current. By adjusting Pm_in, the voltage and frequency output of 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 system frequency; dph iu represents the PWM modulation phase of the DC / AC converter, which determines the phase variation of the PWM signal and is crucial for controlling the phase and frequency of the DC / AC converter's output voltage. By adjusting dph iu, the converter's output voltage can be synchronized with the grid voltage or other reference signals, achieving stable phase and frequency control and ensuring the normal operation of the power system. For example, during grid-connected operation, the phase and frequency of the converter's output voltage must be strictly matched to the grid voltage to achieve efficient and stable energy transmission and power exchange. The specific calculation method may involve the system's rated frequency Fcom and other parameters related to frequency control. By properly designing the dph calculation method, the DC / AC converter's output frequency can be precisely controlled to meet frequency requirements in different application scenarios, such as standard grid frequencies of 50Hz or 60Hz, or flexibly adjusted according to actual needs in specialized 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 effect 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 used to calculate the power angle δ 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 Indicates 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 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 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 for 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] Where 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 fee is as follows:

[0158] First, the operating costs of distributed photovoltaics: Distributed photovoltaics mainly consider the control costs of photovoltaic units, which can be expressed 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 costs of energy storage: The operating costs of energy storage include the cost of energy storage charging and discharging. The specific expression is as follows:

[0162]

[0163] Where, 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 severe overload of DC / AC converter: The penalty fee for severe overload of DC / AC converter reflects the tolerance level for severe overload of DC / AC converter, which is expressed by the penalty fee coefficient:

[0165]

[0166] Where, 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] Where, 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 ith photovoltaic group at the current time t, indicating the actual active power that the ith photovoltaic group can output at the current time t; is the reactive power of the PV group i 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 charge and discharge power constraints are as follows:

[0173]

[0174] Where, Respectively represent the maximum discharge power and maximum charging power of the energy storage unit, Respectively represent the minimum discharge power and minimum charging power of the energy storage unit; the energy storage can be operated at the optimal charging power state by setting the maximum charging power and the minimum charging power; They represent the increased discharge power and charging power of the energy storage unit e at time t respectively; Respectively represent the discharge state and charge state of energy storage, both are 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] Where, represents the SOC of unit e during 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] Where, 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 units; is the active power of the PV group i 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] Where, 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 imbalance 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 imbalance, voltage fluctuation and flicker, and harmonics, and has outstanding advantages in both 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 accomplished by hardware, or 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 to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended 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 is constructed, which consists of an AC / DC converter, three DC / AC converters, and a DC bus in the middle. 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 its output single-phase AC voltage and frequency to ensure the power supply of the load connected to the phase line and the absorption of photovoltaic power. 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: ； Where, 、 、 、 They 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; According to the above calculation, the active power Get the DC / AC converter frequency reference value : ； in, Indicates the rated frequency of the DC / AC converter; Indicates the active frequency droop coefficient; Reactive power output by DC / AC converter The calculation formula is: ； In order to make the reactive power output by the DC / AC converter Do not exceed the allowable value, and add processing for reactive power exceeding the range, specifically: ； ； in, It is a reference value calculated to handle the situation where the reactive power exceeds the upper limit; It is a reference value calculated to handle the situation where the reactive power exceeds the lower limit; 、 They represent the maximum and minimum reactive power outputs allowed by the DC / AC converter respectively; It is a coefficient related to reactive power upper limit control, used to adjust the impact on the voltage reference value when the reactive power approaches the upper limit; It is a coefficient related to reactive power lower limit control, and its role is similar to Similar, but used to handle situations where reactive power is close to the lower limit; 、 They are the maximum power duration period and the minimum power duration period respectively; Then the preliminary reference value of the inverter grid-connected voltage can be determined. And the final inverter power grid voltage reference value : ； in, Indicates the preliminary grid-connected voltage reference value of the inverter power supply; Indicates the rated voltage of the DC / AC converter; is the reactive voltage droop coefficient; Indicates the actual reactive power of the DC / AC converter; Indicates the rated reactive power of the DC / AC converter; ； in, It is the final reference value of the grid-connected voltage of the inverter power supply; The actual value of the grid-connected voltage of the DC / AC converter is: ； Where, Indicates the actual value of the grid-connected voltage of the DC / AC converter, Represents the real part of the actual value of the DC / AC converter grid-connected voltage, Represents the imaginary part of the actual value of the DC / AC converter grid-connected voltage; 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 of the DC / AC converter. ,Right now: ； in, is the proportional time constant of the PI control, is the integral time constant of PI control; PWM modulation phase of DC / AC converter It is calculated by the following formula: ； Where, is the system rated frequency; 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.

2. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 1 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 for 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: ； Where, is the active power reference value of the AC / DC converter, 、 They are the rated voltage and actual voltage of the DC bus at the AC / DC converter end, 、 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: ； in, Represents the grid-connected voltage of the AC / DC converter; 、 、 、 They are the active power reference value, reactive power reference value, actual active power, and actual reactive power of the AC / DC converter; 、 、 、 They are active proportional time constant, active integral time constant, reactive proportional time constant, and reactive integral time constant; 、 They are the rated voltage and actual voltage of the DC bus at the AC / DC converter end; 、 They are the proportional time constant and integral time constant of PI control respectively; 、 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, Indicates the DC bus capacitor voltage; Indicates the total power of the AC / DC converter; Indicates the capacitance value of the DC bus; Represents an imaginary unit, used to express 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 and frequency control is as follows: The existence of rotor inertia of synchronous generator makes it have active frequency droop characteristics. The virtual synchronous machine characteristics of 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: ； ； Where, 、 They are the rated frequency and rated voltage of the DC / AC converter; 、 are the actual frequency and actual voltage of the DC / AC converter respectively; 、 They are the rated active power and rated reactive power of the DC / AC converter respectively; 、 They are the actual active power and actual reactive power of the DC / AC converter respectively; 、 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 1, 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 as well as the action of the PI controller. The droop control coefficient and 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: ； in, is the system angular frequency; represents the inertia of the power system, 、 、 、 They are the rated frequency, rated grid voltage, rated active power and rated reactive power of the DC / AC converter; 、 、 、 、 、 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; 、 Represent the actual active power and actual reactive power of the DC / AC converter respectively.

7. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 1, characterized in that: In step S3, the specific control strategy for the single-phase source-grid-load-storage coordinated optimization control is as follows: In the single-phase source-grid-load-storage coordinated optimization control, the objective function for minimizing the operating cost of photovoltaic, energy storage, and DC / AC converter heavy overload control is expressed as follows: ； Where, represents the goal of minimizing operating cost, express The operating costs of photovoltaic power generation during the period; Represents the operating cost of the energy storage system; Indicates the penalty fee for severe overload of the DC / AC converter.

8. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 7, characterized in that: In the objective function of minimizing operating costs, 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, which can be expressed as follows: ； Where, Indicates the number of photovoltaic units; is the photovoltaic grid-connected electricity price; Indicates the unit exist The regulated power of the time period, unit: kW; The duration of a period, unit: hours; Second, the operating costs of energy storage: The operating costs of energy storage include the cost of energy storage charging and discharging. The specific expression is as follows: ； Where, 、 、 Represents the energy storage charging and discharging price Time value, daily minimum value, daily maximum value, unit: yuan / kWh; 、 Respectively represent the units Increased discharge power and charging power, unit: kW; Indicates the number of energy storage units; Third, the penalty fee for severe overload of DC / AC converter: The penalty fee for severe overload of DC / AC converter reflects the tolerance level for severe overload of DC / AC converter, which is expressed by the penalty fee coefficient: ； Where, is the overload power of the DC / AC converter, is the penalty cost coefficient.

9. The novel low-voltage multi-port single-phase power supply equipment control method according to claim 8, characterized in that: The objective function of minimizing the running cost should satisfy the following constraints: 1) Photovoltaic constraints: ； ； Where, For the Photovoltaic Group The regulated active power at the time of Photovoltaic Group The active power adjusted relative to its initial operating state or the operating state at the previous moment; For the Group photovoltaic in the current The active power at the moment, indicating the Group PV at the current moment The actual active power that can be output; For the Photovoltaic Group Reactive power at time ; For the Apparent power of each inverter; For the The maximum power angle of the photovoltaic group; 2) Energy storage constraints include charge and discharge constraints and SOC constraints; A. The charge and discharge power constraints are as follows: ； Where, 、 Respectively represent the maximum discharge power and maximum charging power of the energy storage unit, 、 Respectively represent the minimum discharge power and minimum charging power of the energy storage unit; 、 Represents energy storage units At the moment Increased discharge power and charging power; 、 Respectively represent the discharge state and charge state of energy storage, both are 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: ； Where, Indicates the unit exist SOC of the time period, Indicates the unit exist SOC of the time period, 、 Respectively represent the maximum and minimum allowable values ​​of SOC; Indicates the unit exist The charge and discharge power at the moment, charging is positive and discharging is negative; represents the initial capacity of SOC, Indicates the SOC capacity of the last period; 3) Power balance constraints: ； Where, For the Energy storage in the current Active power at the moment; is the number of energy storage units; For the Group photovoltaic in the current Active power at the moment; is the number of photovoltaic units; For the current Active power of load at any moment; For the current Active power of DC / AC converter at the moment and overload power of DC / AC converter The following constraints are met: ； Where, is the rated power of the DC / AC converter.

Images