阅读说明：本技术 一种孤岛储能型功率单元串联微电网结构及控制方法 (Island energy storage type power unit series micro-grid structure and control method ) 是由 刘晓晖 何晋伟 于 2019-08-19 设计创作，主要内容包括：本发明公开一种孤岛储能型功率单元串联微电网结构及控制方法,由多个功率单元串联组成,功率单元包括直流储能单元、直流/交流转换电路和采样电路,直流储能单元由直流母线电容与储能电池并联而成；直流/交流转换电路包括主功率变换电路及滤波电路,采样电路包括对每个功率单元滤波电感输出电流的采样电路、滤波电容输出电压的采样电路以及对相应直流储能单元内的储能电池信息采样电路；还涉及上述微电网结构的功率控制方法。本发明的优点在于：该微电网结构只需要单级功率变换,减少了系统成本,提高了转换器的效率,同时可以合理利用直流侧电源能量,提高直流储能单元使用寿命。(The invention discloses an island energy storage type power unit series micro-grid structure and a control method, wherein a plurality of power units are connected in series to form the island energy storage type power unit series micro-grid structure, each power unit comprises a direct current energy storage unit, a direct current/alternating current conversion circuit and a sampling circuit, and the direct current energy storage unit is formed by connecting a direct current bus capacitor and an energy storage battery in parallel; the direct current/alternating current conversion circuit comprises a main power conversion circuit and a filter circuit, and the sampling circuit comprises a sampling circuit for outputting current to a filter inductor of each power unit, a sampling circuit for outputting voltage to a filter capacitor, and an energy storage battery information sampling circuit in a corresponding direct current energy storage unit; also relates to a power control method of the micro-grid structure. The invention has the advantages that: the micro-grid structure only needs single-stage power conversion, reduces the system cost, improves the efficiency of the converter, can reasonably utilize the energy of a direct-current side power supply, and prolongs the service life of a direct-current energy storage unit.)

1. an island energy storage type micro-grid structure with power units connected in series is applied to a micro-grid system which uses an H bridge unit formed by IGBTs as a main power inverter circuit to provide stable and continuous power supply for a load, and is characterized by being formed by connecting at least two power units in series, wherein each power unit comprises a direct current energy storage unit, a direct current/alternating current conversion circuit and a sampling circuit, and the direct current energy storage unit is formed by connecting a direct current bus capacitor and an energy storage battery in parallel; the direct current/alternating current conversion circuit comprises a main power conversion circuit and a filter circuit, wherein the filter circuit consists of a filter inductor and a filter capacitor, the input end of the filter inductor is connected with one end of the main power inverter circuit, the output end of the filter inductor is connected with the input end of the filter capacitor and is connected to one end of a common connection point or the output end of the filter capacitor of another power unit, and the output end of the filter capacitor is connected with the output end of the filter inductor of another power unit or is connected to the other end of the common connection point; the sampling circuit comprises a sampling circuit for outputting current to a filter inductor of each power unit, a sampling circuit for outputting voltage to a filter capacitor and an energy storage battery information sampling circuit in a corresponding direct current energy storage unit, wherein information obtained by sampling of the sampling circuit is transmitted into a local controller of the power unit through a signal line, the sampling circuit further comprises a sampling circuit for voltage on two sides of a load at a common connection point, the sampling circuit flows through the load current, and the information obtained by sampling is transmitted to a central controller through the signal line.

2. A control method based on an island energy storage type power unit series micro-grid structure is characterized by comprising the following steps:

(1) The central controller of the public connection point compensates the voltage at two sides of the load through the proposed amplitude proportional-integral recovery control algorithm, and sends the gain factor obtained by calculation to the local controller of each power unit in a low-bandwidth communication mode;

(2) The central controller samples the voltage on two sides of the load at the common connection point and the current flowing through the load to calculate the load power factor at the common connection point, calculates the weighting factor of each power unit according to the energy storage battery information uploaded by the local controller, and sends the load power factor and the weighting factor to the local controllers of the corresponding power units in a low-bandwidth communication mode;

(3) The local controller of each power unit calculates the power factor of each power unit according to the sampled output current of the filter inductor and the sampled output voltage of the filter capacitor, adjusts the intercept of inverse power factor control by combining the weighting factor received from the central controller and the load power factor, adjusts the amplitude of the output voltage by the gain factor received from the central controller, further generates the reference voltage of the power unit, and adopts double closed loop tracking of a voltage outer loop and a current inner loop to realize power control of the proportion of the active power output by each power unit and the information of the energy storage battery in the direct current energy storage unit, and simultaneously automatically eliminates the voltage frequency deviation of a common connection point.

3. The method for controlling the islanded energy storage type power unit series microgrid structure-based according to claim 2, characterized in that the step (1) specifically comprises the following steps:

a) Sampling voltages on two sides of a load at a common connection point by using a voltage sensor, calculating to obtain voltage amplitudes on two sides of the load at the common connection point, comparing the voltage amplitudes with rated voltage amplitudes on two sides of the load at the common connection point, and calculating to obtain a gain factor through an amplitude proportional-integral recovery control algorithm according to the result:

Wherein E^*And E_PCCRespectively the amplitudes of rated voltage and measured voltage at two sides of a load at a common connecting point; k is a radical of_{p_mag}And k_{i_mag}Respectively, the proportional gain and the integral gain of the amplitude proportional-integral recovery control algorithm; s is a derivative term of the controller; the output of the controller is a gain factor g_c；

b) the gain factor is transmitted to a local controller of the power unit through low-bandwidth communication, and the local controller of the power unit generates a reference voltage amplitude of the corresponding power unit to realize voltage amplitude compensation on two sides of a load of a common connection point:

Wherein G is_delay(s) is the transfer function of the low bandwidth communication, τ_mIs the delay, g, of the low bandwidth communication of power cell m_{c_Local，m}is a gain factor received by the local controller after low bandwidth communication; e_mIs the power cell reference voltage amplitude generated by the local controller, and k is the total number of power cells in series.

4. The island energy storage type power unit series micro grid structure-based control method of claim 2, wherein the step (2) comprises the following steps: the central controller samples the voltage V on both sides of the load at the common connection point_PCCCurrent I through the load_LoadCalculating the load power factor PF at the common connection point_LoadAnd the energy storage battery information SoC from the local controller is collected_mAnd calculating a weighting factor:

W_SoC,m＝k·SoC_m/∑_m＝1,2...,kSoC_m (1-4)

Wherein the SoC_mSoC (state of charge) of power unit m, m is 1,2 … k is power unit 1, power unit 2 is connected in series to total number k, W of power units_SoC，mIs the calculated weighting factor.

5. The island energy storage type power unit series micro grid structure-based control method of claim 2, wherein the step (3) comprises the following stepsThe method comprises the following steps: the local controllers of the power units receive the weighting factors W from the central controller according to the calculated power factors of the corresponding power units_SoC，mAnd a load power factor PF at the common connection point_LoadAdjusting the intercept of the inverse power factor control to generate the angular frequency of the reference voltage of the power unit:

ω_m＝ω^*+D_PF·(PF_m-W_SoC,m·PF_Load) (1-5)

Wherein, ω is^*Is the rated output angular frequency, PF_mIs the calculated power factor, D, of the corresponding power cell m_PFIs the inverse sag factor, PF_Loadis the point of common coupling load power factor.

The local controller generates a reference voltage according to the angular frequency of the reference voltage of the power unit and the amplitude of the reference voltage of the power unitFor the reference voltage value, the voltage outer ring adopts quasi-resonance control through double closed-loop tracking of a voltage outer ring and a current inner ring, and the transfer function of the voltage outer ring is G_v(s) one input of the outer loop is the sampled filter capacitor output voltage V_cThe other input is a reference voltageThe output of the outer ring is a reference currentThe transfer function of the inner loop is G_I(s) one input of the inner loop is a sampled filter inductor output current I_oThe other input is the reference current output by the outer ringThe inner loop output is a modulated voltage for modulation

G_I(s)＝k_Inner (1-7)

in the formula k_pIs the proportional gain, k_i，hThe gain of the quasi-resonance controller is h, h is f,3,5,7,9 is the harmonic number which can be the fundamental wave, 3 harmonic, 5 harmonic, 7 harmonic, 9 harmonic, omega_cIs the bandwidth angular frequency, omega, of the quasi-resonant controller_hIs the angular frequency, k, of the quasi-resonant controller at harmonic order h_InnerIs the proportional gain of the inner loop.

Technical Field

The invention relates to the field of isolated island operation micro-grids, in particular to an isolated island energy storage type power unit series micro-grid structure and a control method, wherein reverse power factor control capable of adjusting intercept is carried out in a cooperative control mode to realize dispersed proportional active power control and public connection point voltage management.

Background

The power generation proportion of new energy is increased, and a large amount of distributed renewable energy and energy storage units thereof are connected to the microgrid, so that the development of the microgrid for island operation is promoted. In past researches, an island-running micro-grid is formed by connecting a plurality of inverters in parallel, however, the voltage level of a distributed direct-current power supply is smaller than the grid-connected voltage level under common conditions, and the parallel inverters need to be boosted through two-stage power conversion to reach the grid-connected voltage level. The multi-inverter parallel system generally adopts droop control to realize power sharing without communication, but the droop control has the problems of instability, inaccurate reactive power distribution and the like. On the other hand, a series inverter has been proposed, which directly connects a low-voltage-class dc power supply to a grid through primary power conversion, and which is an important means for connecting renewable energy to a grid.

Past research has focused on grid-tied operation of the inverter. The synchronization of all inverters is completed by using one central controller, however, for a microgrid which is far away and runs in an isolated island and is composed of a large number of direct current power supplies, the use of the central controller is difficult to control, the cost is high, and the reliability is poor. In addition, since the parallel cells and the series cells have different power flow patterns, it is difficult to apply droop control to the parallel system to the series system.

In order to overcome these difficulties, it is urgently needed to provide a structure which only needs single-stage power conversion and connects an energy storage unit into a microgrid, and a power distribution and voltage management control method with high reliability.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides an island energy storage type power unit series micro-grid structure and a control method.

The purpose of the invention is realized by the following technical scheme:

An island energy storage type micro-grid structure with power units connected in series is applied to a micro-grid system which uses an H bridge unit formed by IGBTs as a main power inverter circuit to provide stable and continuous power supply for a load, and is formed by connecting at least two power units in series, wherein each power unit comprises a direct current energy storage unit, a direct current/alternating current conversion circuit and a sampling circuit, and the direct current energy storage unit is formed by connecting a direct current bus capacitor and an energy storage battery in parallel; the direct current/alternating current conversion circuit comprises a main power conversion circuit and a filter circuit, wherein the filter circuit consists of a filter inductor and a filter capacitor, the input end of the filter inductor is connected with one end of the main power inverter circuit, the output end of the filter inductor is connected with the input end of the filter capacitor and is connected to one end of a common connection point or the output end of the filter capacitor of another power unit, and the output end of the filter capacitor is connected with the output end of the filter inductor of another power unit or is connected to the other end of the common connection point; the sampling circuit comprises a sampling circuit for outputting current to a filter inductor of each power unit, a sampling circuit for outputting voltage to a filter capacitor and an energy storage battery information sampling circuit in a corresponding direct current energy storage unit, wherein information obtained by sampling of the sampling circuit is transmitted into a local controller of the power unit through a signal line, the sampling circuit further comprises a sampling circuit for voltage on two sides of a load at a common connection point, the sampling circuit flows through the load current, and the information obtained by sampling is transmitted to a central controller through the signal line.

In addition, another technical scheme is provided, namely a control method based on an island energy storage type power unit series micro-grid structure, which comprises the following steps:

(1) the central controller of the public connection point compensates the voltage at two sides of the load through the proposed amplitude proportional-integral recovery control algorithm, and sends the gain factor obtained by calculation to the local controller of each power unit in a low-bandwidth communication mode;

(2) The central controller samples the voltage on two sides of the load at the common connection point and the current flowing through the load to calculate the load power factor at the common connection point, calculates the weighting factor of each power unit according to the energy storage battery information uploaded by the local controller, and sends the load power factor and the weighting factor to the local controllers of the corresponding power units in a low-bandwidth communication mode;

(3) The local controller of each power unit calculates the power factor of each power unit according to the sampled output current of the filter inductor and the sampled output voltage of the filter capacitor, adjusts the intercept of inverse power factor control by combining the weighting factor received from the central controller and the load power factor, adjusts the amplitude of the output voltage by the gain factor received from the central controller, further generates the reference voltage of the power unit, and adopts double closed loop tracking of a voltage outer loop and a current inner loop to realize power control of the proportion of the active power output by each power unit and the information of the energy storage battery in the direct current energy storage unit, and simultaneously automatically eliminates the voltage frequency deviation of a common connection point.

Further, the step (1) specifically comprises the following steps:

a) Sampling voltages on two sides of a load at a common connection point by using a voltage sensor, calculating to obtain voltage amplitudes on two sides of the load at the common connection point, comparing the voltage amplitudes with rated voltage amplitudes on two sides of the load at the common connection point, and calculating to obtain a gain factor through an amplitude proportional-integral recovery control algorithm according to the result:

Wherein E^*And E_PCCRespectively the amplitudes of rated voltage and measured voltage at two sides of a load at a common connecting point; k is a radical of_{p_mag}And k_{i_mag}Respectively, the proportional gain and the integral gain of the amplitude proportional-integral recovery control algorithm; s is a derivative term of the controller; the output of the controller is a gain factor g_c；

b) The gain factor is transmitted to a local controller of the power unit through low-bandwidth communication, and the local controller of the power unit generates a reference voltage amplitude of the corresponding power unit to realize voltage amplitude compensation on two sides of a load of a common connection point:

Wherein G is_delay(s) is the transfer function of the low bandwidth communication, τ_mis the delay, g, of the low bandwidth communication of power cell m_{c_Local，m}Is a gain factor received by the local controller after low bandwidth communication; e_mIs the power cell reference voltage amplitude generated by the local controller, and k is the total number of power cells in series.

Further, the step (2) comprises the following steps: the central controller samples the voltage V on both sides of the load at the common connection point_PCCCurrent I through the load_LoadCalculating the load power factor PF at the common connection point_Loadand the energy storage battery information SoC from the local controller is collected_mAnd calculating a weighting factor:

W_SoC，m＝k·SoC_m/∑_{m＝1，2...，k}SoC_m (1-4)

Wherein the SoC_mIs the SoC (state of charge) of power unit m, m 1, 2.. k is power unit 1, power unit 2 up to the total number k, W of series-connected power units_SoC，mIs the calculated weighting factor.

Further, the step (3) comprises the following steps: the local controllers of the power units receive the weighting factors W from the central controller according to the calculated power factors of the corresponding power units_SoC，mAnd a load power factor PF at the common connection point_Loadadjusting the intercept of the inverse power factor control to generate the angular frequency of the reference voltage of the power unit:

ω_m＝ω^*+D_PF·(PF_m-W_SoC，m·PF_Load) (1-5)

Wherein, ω is^*Is the rated output angular frequency, PF_mIs the calculated power factor, D, of the corresponding power cell m_PFIs the inverse sag factor, PF_LoadIs the point of common coupling load power factor.

The local controller generates a reference voltage according to the angular frequency of the reference voltage of the power unit and the amplitude of the reference voltage of the power unitFor the reference voltage value, the voltage outer ring adopts quasi-resonance control through double closed-loop tracking of a voltage outer ring and a current inner ring, and the transfer function of the voltage outer ring is G_v(s) one input of the outer loop is the sampled filter capacitor output voltage V_cThe other input is a reference voltageThe output of the outer ring is a reference currentThe transfer function of the inner loop is G_I(s) one input of the inner loop is a sampled filter inductor output current I_oThe other input is the reference current output by the outer ringThe inner loop output is a modulated voltage for modulation

G_I(s)＝k_Inner(1-7) formula (II) wherein k_pIs the proportional gain, k_i，hThe gain of the quasi-resonance controller is h, h is f,3,5,7,9 is the harmonic number which can be the fundamental wave, 3 harmonic, 5 harmonic, 7 harmonic, 9 harmonic, omega_cIs the bandwidth angular frequency, omega, of the quasi-resonant controller_hIs the angular frequency, k, of the quasi-resonant controller at harmonic order h_Inneris the proportional gain of the inner loop.

compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. the energy storage type power unit series micro-grid structure is characterized in that a plurality of power units are connected in series, and the energy storage type power unit series micro-grid structure is different from a traditional multi-inverter parallel grid-connection mode.

2. The single-stage power conversion with the specific series structure reduces the requirement of the power unit on the level of the direct current side input voltage, improves the utilization rate of new energy, and reduces the requirement of a grid-connected system on the new energy.

3. The inherent circuit property of the series connection mode among the power units ensures that the output currents of the power units are constant and equal, the problem of circulation does not exist, the use of the circulation restraining equipment of the traditional grid-connected inverter is avoided, and the cost is reduced.

4. The power control method has the characteristics of simplicity and practicality, only local current signals and voltage signals of the power units need to be acquired, communication among the power units is not needed, and parameters of the micro-grid system do not need to be acquired; the power unit can output active power and reactive power in proportion and accurately according to the energy of a power supply at the direct current side, so that the problem of reasonably and accurately distributing power according to the energy at the direct current side in the traditional island micro-grid is solved.

Drawings

Fig. 1 is a schematic diagram of a microgrid structure according to the present invention.

fig. 2 is a flow chart of cooperative control based on the energy storage type power unit series micro-grid structure of the present invention.

Fig. 3 is an experimental waveform diagram.

Detailed Description

the invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in figures 1 and 2An island energy storage type power unit series micro-grid structure is formed by connecting three power units in series, wherein each power unit comprises a direct current energy storage unit 1, a direct current/alternating current conversion circuit 2 and a sampling circuit 3. The DC energy storage unit is composed of a DC bus capacitor C_dIs connected with the energy storage battery in parallel; the DC/AC conversion circuit comprises a main power conversion circuit and a filter circuit, wherein the filter circuit consists of a filter inductor L_fAnd a filter capacitor C_fComponent, filter inductance L_fThe input end of the filter is connected with one end of the main power inverter circuit, and the filter inductor L_fOutput terminal and filter capacitor C_fIs connected to the input terminal of the power unit and is connected to one end of the common connection point or the filter capacitor C of another power unit_fOf the filter capacitor C_fAnd the filter inductance L of another power unit_fThe output end of the first switch is connected with or connected to the other end of the common connection point; the sampling circuit comprises a filter inductor L for each power unit_fSampling circuit of output current and filter capacitor C_fThe sampling circuit outputs voltage and samples the energy storage battery information in the corresponding direct current energy storage unit, the information obtained by sampling is transmitted to a local controller of the power unit through a signal wire, the sampling circuit also comprises a sampling circuit for the voltage on two sides of a load at a common connection point and a sampling circuit for the current flowing through the load, and the information obtained by sampling is transmitted to the central controller through the signal wire.

The patent refers to the field of 'control or regulating systems and its monitoring or testing arrangements'.

The method comprises the following steps that firstly, voltage sensors are used for sampling voltages on two sides of a load at a common connection point, voltage amplitudes on two sides of the load at the common connection point are obtained through calculation and are compared with rated voltage amplitudes on two sides of the load at the common connection point, and a gain factor is obtained through calculation of the result through an amplitude proportional-integral recovery control algorithm:

Wherein E^*And E_PCCRespectively rated on both sides of the load at the common connection pointVoltage and amplitude of the measured voltage, in the experiment E^*Is set to 120; k is a radical of_{p_mag}And k_{i_mag}respectively setting the proportional gain and the integral gain of an amplitude proportional-integral recovery control algorithm as 0.12/V and 0.008/(V.s) respectively according to the requirements of response speed and stability in an experiment; s is a derivative term of the controller; the output of the controller is a gain factor g_c. The gain factor is transmitted to a local controller of the power unit through low-bandwidth communication, and the local controller of the power unit generates a reference voltage amplitude of the corresponding power unit to realize voltage amplitude compensation on two sides of a load of a common connection point:

wherein G is_delay(s) is the transfer function of the low bandwidth communication, τ_mis the delay, g, of the low bandwidth communication of power cell m_{c_Local，m}Is a gain factor received by the local controller after low bandwidth communication; e_mIs the power cell reference voltage amplitude generated by the local controller, and k is the total number of power cells in series.

Second, the central controller samples the voltage V on both sides of the load at the common connection point_PCCCurrent I through the load_Loadcalculating the load power factor PF at the common connection point_LoadAnd the energy storage battery information SoC from the local controller is collected_mAnd calculating a weighting factor:

W_SoC，m＝k·SoC_m/∑_{m＝1，2...，k}SoC_m (4)

Wherein the SoC_mIs SoC (state of charge) of power unit m, where m is 1, 2.. k is power unit 1, power unit 2 is up to total number k of series-connected power units, and in this experiment, 3, W is set_SoC，mIs the calculated weighting factor.

third, the local controller of the power unit is based on the calculationThe resulting power factor of the corresponding power cell, the weighting factor W received from the central controller_SoC，mAnd a load power factor PF at the common connection point_LoadAdjusting the intercept of the inverse power factor control to generate the angular frequency of the reference voltage of the power unit:

ω_m＝ω^*+D_PF·(PF_m-W_SoC，m·PF_Load) (5)

Wherein, ω is^*Is the rated output angular frequency, which is set to 100 π rad/s, PF in this example_mis the calculated power factor, D, of the corresponding power cell m_PFis the inverse droop coefficient, which is set to 10rad/s, PF in this experiment_LoadIs the point of common coupling load power factor. The local controller generates a reference voltage according to the angular frequency of the reference voltage of the power unit and the amplitude of the reference voltage of the power unitFor the reference voltage value, the voltage outer ring adopts quasi-resonance control through double closed-loop tracking of a voltage outer ring and a current inner ring, and the transfer function of the voltage outer ring is G_v(s) one input of the outer loop is the sampled filter capacitor output voltage V_cThe other input is a reference voltageThe output of the outer ring is a reference currentThe transfer function of the inner loop is G_I(s) one input of the inner loop is a sampled filter inductor output current I_oThe other input is the reference current output by the outer ringThe inner loop output is a modulated voltage for modulation

G_I(s)＝k_Inner (7)

In the formula k_pIs the proportional gain, set to 0.2A/V, k in this experiment_i，hThe gain of the quasi-resonance controller is h, the harmonic times h are f,3,5,7 and 9 are fundamental waves, 3 harmonic waves, 5 harmonic waves, 7 harmonic waves and 9 harmonic waves, in the experiment, k is the fundamental wave, 3 harmonic waves, 5 harmonic waves, 7 harmonic waves and 9 harmonic waves_i，fSet to 30A/(V.s), k_i，3And k_i，5，k_i，7，k_i，9Set as 15A/(V.s), omega_cThe bandwidth angular frequency of the quasi-resonant controller is set to be 4rad/s in the experiment; omega_hIs the angular frequency, k, of the quasi-resonant controller at harmonic order h_InnerIs the proportional gain of the inner loop, set to 15V/A in this experiment.

In conclusion, the method realizes that the amplitude frequency of the voltage of the output common connection point is effectively managed under the condition without a high-frequency communication line, all series inverters are synchronized, and the inverters perform accurate active power distribution according to the energy stored by the rear-stage direct-current side battery.

As shown in the experimental waveform of fig. 3, each grid is 1s, 2.5s is taken as the duration of each stage, the first stage is not controlled, the second stage adopts the traditional full-dispersion anti-droop control, the third stage starts the control method of the invention, at this time, the SoC ratio of the energy storage battery in each power unit direct current energy storage unit is 4: 3, the accurate active power distribution (4: 3) is realized according to the experimental data, meanwhile, the voltage amplitudes at two sides of the load meet the power supply voltage requirement, and the load of the fourth stage is suddenly changed.

The present invention is not limited to the above-described embodiments. The foregoing description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above specific embodiments are merely illustrative and not restrictive. Those skilled in the art can make many changes and modifications to the invention without departing from the spirit and scope of the invention as defined in the appended claims.