A control method and device for off-grid parallel operation of multiple energy storage converters

Abstract

The present application discloses a multi-energy storage converter off-grid parallel operation control method and control device, which improves the operation stability of the parallel system. The method includes: determining one of the multiple energy storage converters of the energy storage power station as the host, and the rest as slaves; the host performs power outer loop, voltage middle loop, and current inner loop control according to the load power of the entire station, and its power outer loop adopts droop control, and the output of its power outer loop and voltage middle loop is sent to each slave; the slave performs power outer loop, voltage middle loop, and current inner loop control according to the output of the host's power outer loop and voltage middle loop; the slave's power outer loop adopts droop control, and the given value of the slave's voltage middle loop is the sum of the output of the host's power outer loop and the first compensation value, and the given value of the slave's current inner loop is the sum of the output of the host's voltage middle loop and the second compensation value, the first compensation value is calculated based on the output of the slave's power outer loop, and the second compensation value is calculated based on the output of the slave's voltage middle loop.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and more specifically, to a method and device for controlling off-grid parallel operation of multiple energy storage converters. Background Art

[0002] The energy storage inverter is a device connected between the battery pack and the power grid and / or load to realize bidirectional conversion of electric energy. It can control the charging and discharging process of the battery pack, perform AC / DC conversion, and directly power the load in an off-grid state.

[0003] In view of the limitation of the maximum capacity of a single energy storage inverter, energy storage power stations usually use multiple energy storage inverters to operate in parallel to increase the total capacity of the entire station. However, when multiple energy storage inverters are operated in parallel off-grid, uneven current is prone to occur. The energy storage inverter with the largest current output is prone to overcurrent faults, affecting the stable operation of the off-grid parallel system of multiple energy storage inverters. Summary of the invention

[0004] In view of this, the present invention provides a method and a control device for off-grid parallel operation of multiple energy storage converters to improve the operating stability of the parallel system.

[0005] A method for controlling off-grid parallel operation of multiple energy storage converters, comprising:

[0006] Determine one of the multiple energy storage converters in the energy storage power station as the master, and the others as slaves;

[0007] The host performs three-loop control of the power outer loop, voltage middle loop, and current inner loop according to the load power of the entire station to obtain the host PWM signal; the host's power outer loop adopts a droop control strategy, and the outputs of the host's power outer loop and voltage middle loop are sent to each slave;

[0008] The slave performs three-loop control of the power outer loop, voltage middle loop and current inner loop according to the output of the power outer loop and voltage middle loop of the host to obtain the slave PWM signal; wherein the power outer loop of the slave adopts a droop control strategy, the given value of the voltage middle loop of the slave is the sum of the output of the power outer loop of the host and the first compensation value, the given value of the current inner loop of the slave is the sum of the output of the voltage middle loop of the host and the second compensation value, the first compensation value is calculated based on the output of the power outer loop of the slave, and the second compensation value is calculated based on the output of the voltage middle loop of the slave.

[0009] Optionally, determining one of the multiple energy storage converters as a master and the others as slaves includes:

[0010] Obtain the remaining power SOC of the battery pack connected to each energy storage converter respectively;

[0011] When each battery pack is in a discharging state, the energy storage converter corresponding to the battery pack with the largest SOC is set as the master, and the others are set as slaves;

[0012] When each battery pack is in a charging state, the energy storage converter corresponding to the battery pack with the smallest SOC is set as the master, and the others are set as slaves.

[0013] Optionally, the host performs power outer loop control, including:

[0014] The host performs power calculation based on the load three-phase voltage and load three-phase current to obtain the load active power PL and load reactive power QL;

[0015] The host calculates its own voltage angular frequency ω and voltage given value U, and integrates the voltage angular frequency ω to obtain the voltage phase angle given value θ of the host; the voltage given value U and the voltage phase angle given value θ of the host are the outputs of the power outer loop of the host, and are sent to each slave;

[0016] Among them, the calculation formulas of the voltage phase angle given value θ and the voltage given value U are as follows:

[0017] ω=(Pref-PL)×mp+ω o ,

[0018] U=(Qref-QL)×mq+U o ;

[0019] Where Pref represents the total active power given value of the entire station issued by the energy management system EMS of the energy storage power station, Qref represents the total reactive power given value of the entire station issued by EMS, mp represents the active droop coefficient, mq represents the reactive droop coefficient, ω o Indicates the rated angular frequency, U o Indicates rated voltage.

[0020] Optionally, the host performs voltage mid-loop control, including:

[0021] The host calculates the voltage command according to the voltage given value U and the voltage phase angle given value θ, and obtains the host's α-axis voltage given value U×sinθ and β-axis voltage given value U×cosθ; and the host performs Clark transformation on its own three-phase voltage V to obtain the host's α-axis voltage feedback value U 1α and β-axis voltage feedback value U 1β ;

[0022] The host converts the α-axis voltage given value U×sinθ and the α-axis voltage feedback value U 1α The difference is input into the host voltage loop controller to obtain the α-axis voltage U output by the host voltage loop controller 1α *; The β-axis voltage given value U×cosθ and the β-axis voltage feedback value U 1β The difference is input into the host voltage loop controller to obtain the β-axis voltage U output by the host voltage loop controller 1β * ; α axis voltage U 1α * and β-axis voltage U 1β * It is the output of the host voltage loop and is sent to each slave.

[0023] Optionally, the host performs current inner loop control, including:

[0024] The host performs Clark transformation on its own three-phase current I to obtain the host α-axis current feedback value I 1α and the host β-axis current feedback value I 1β ;

[0025] The host will α axis voltage U 1α * and the α-axis current feedback value I 1α The difference is input into the host current loop controller to obtain the α-axis current signal I output by the host current loop controller 1α * ; Set the β axis voltage U 1β * and the β-axis current feedback value I 1β The difference is input into the host current loop controller to obtain the β-axis current I output by the host current loop controller 1β * ;α-axis current signal I 1α * and β-axis current I 1β * It is the output of the host's current inner loop and is used to control the PWM controller to generate the host's PWM wave.

[0026] Optionally, the control logic of each slave is the same, and slave 1 is one of the slaves. Slave 1 performs power outer loop control, including:

[0027] Slave 1 performs power calculation based on its own three-phase voltage V2abc and three-phase current I2abc to obtain active power P2 and reactive power Q2 of slave 1;

[0028] Slave 1 calculates its own voltage angular frequency ω2 and voltage given value U2 * , and integrate the voltage angular frequency ω2 to obtain the voltage phase angle given value θ2 * ; Voltage setting value U2 of slave 1 * And the voltage phase angle given value θ2 * is the output of the power outer loop of slave 1;

[0029] Among them, the voltage angular frequency ω2 and the voltage set value U2 * The calculation formula is as follows:

[0030] ω2=(P2ref-P2)×mp2+ω o ,

[0031] U2 * =(Q2ref-QL)×mq2+U o ;

[0032] Where P2ref represents the active power given value of slave 1 sent by EMS, Q2ref represents the reactive power given value of slave 1 sent by EMS, mp2 represents the active power droop coefficient of slave 1, mq2 represents the reactive power droop coefficient of slave 1, ω o Indicates the rated angular frequency, U o Indicates rated voltage.

[0033] Optionally, slave 1 performs voltage mid-loop control, including:

[0034] Slave 1 calculates its own voltage given value U2 and phase angle given value θ2, and the calculation formula is as follows:

[0035] U2=m2×U2 * +m1×U,

[0036] θ2=m2×θ2 * +m1×θ;

[0037] In the formula, m1 and m2 are constants;

[0038] Slave 1 calculates the voltage command according to the voltage given value U2 and the phase angle given value θ2, and obtains the α-axis voltage given value U2×sinθ2 and the β-axis voltage given value U2×cosθ2 of slave 1; and slave 1 performs Clark transformation on its own three-phase voltage V2abc to obtain the α-axis voltage feedback value U of slave 1. 2α and the β-axis voltage feedback value U of slave 1 2β ;

[0039] Slave 1 converts the α-axis voltage given value U2×sinθ2 into the α-axis voltage feedback value U 2α The difference is input into the voltage loop controller of slave 1, and the α-axis voltage U output by the voltage loop controller of slave 1 is obtained. 2α * ; The β-axis voltage given value U2×cosθ2 and the β-axis voltage feedback value U 2β The difference is input into the voltage loop controller of slave 1, and the β-axis voltage U output by the voltage loop controller of slave 1 is obtained. 2β * ; U 2α * and U2β * As the output value of the slave 1 voltage middle loop, the output value of the slave 1 voltage middle loop is the given value of the slave 1 current inner loop.

[0040] Optionally, slave 1 performs current inner loop control, including:

[0041] Slave 1 calculates its own α-axis current loop given value I 2αref and the β-axis current loop given value I 2βref , and its calculation formula is as follows:

[0042]

[0043]

[0044] In the formula, k2 is a constant, k1 is a proportional gain coefficient, and T is an integral time constant;

[0045] Slave 1 performs Clark transformation on its own three-phase current I2abc to obtain the α-axis current feedback value I of slave 1 2α and the β-axis current feedback value I 2β The α-axis current loop given value I of slave 1 2αref and the α-axis current feedback value I 2α The difference is input into the current loop controller of slave 1 to obtain the α-axis current signal I output by the current loop controller of slave 1. 2α * , set the β-axis voltage of slave 1 to I 2βref and the β-axis current feedback value I 2β The difference is input into the current loop controller of slave 1 to obtain the β-axis current I output by the current loop controller of slave 1. 2β * ;α-axis current signal I 2α * and β-axis current I 2β * It is the output of the current inner loop of slave 1 and is used to control the PWM controller to generate the PWM wave of slave 1.

[0046] Optionally, the host voltage loop controller and the slave 1 voltage loop controller are both proportional resonant controllers, and the host current loop controller and the slave 1 current loop controller are both proportional-integral resonant controllers.

[0047] A multi-energy storage converter off-grid parallel operation control device comprises: a processor and a memory, wherein the memory stores a program, and when the program is executed by the processor, any of the multi-energy storage converter off-grid parallel operation control methods described above is implemented.

[0048] It can be seen from the above technical solution that the present invention selects one of the multiple energy storage converters in the whole station as the host and the rest as slaves. The host sends a unified control instruction to all the slaves (i.e., the output of the power outer loop and the voltage middle loop of the host), and the slaves are controlled according to the unified instruction of the host, so that the whole station is integrated into a whole, and unified and coordinated control of the whole station is realized. At this time, it is easy to realize current equalization control to avoid unstable operation of the parallel system caused by uneven current distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 A schematic structural diagram of a multi-energy storage converter off-grid parallel system disclosed in an embodiment of the present invention;

[0051] Figure 2 A flow chart of a method for controlling off-grid parallel operation of multiple energy storage converters disclosed in an embodiment of the present invention;

[0052] Figure 3 A control principle block diagram of a host disclosed in an embodiment of the present invention;

[0053] Figure 4 This is a control principle block diagram of a slave machine 1 disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to promote the energy transformation and green development of the power industry, the penetration rate of renewable energy represented by wind power and photovoltaic power is increasing. However, renewable energy is characterized by randomness, intermittency and volatility, so energy storage is needed to smooth the energy fluctuations between source, grid and load (i.e. power supply, grid and load). The energy storage converter (PCS) is the core equipment of the energy storage system. In addition to the traditional functions of charging and discharging the battery pack, it also needs to have off-grid power supply functions for many important loads. For example, for factories and commercial buildings or remote mountainous areas and islands, it is necessary to ensure that the energy storage converter can continue to provide emergency power supply for factories and commercial buildings or ensure the normal living electricity consumption of residents in mountainous areas and islands when the grid fails, so as to minimize the losses caused by grid failures.

[0055] In view of the limitation of the maximum capacity of a single energy storage converter, energy storage power stations usually use multiple energy storage converters in parallel to increase the total capacity of the entire station. Figure 1 As shown, it includes: multiple energy storage converters, the input end of each energy storage converter is independently connected to a battery pack, and the output end of each energy storage converter is connected in parallel to a load R and / or a feeding device (the feeding device is not in Figure 1 As shown in the figure, the power grid is connected to the power grid through the grid-connected switch QF; the feeding equipment includes, for example, photovoltaic power generation equipment and / or wind power generation equipment, and the feeding equipment can form a microgrid; different from the microgrid, the power grid connected through the grid-connected switch QF is generally also called a large power grid; the electrical topology of each energy storage converter is consistent, and the energy storage converter includes a power unit, a filter inductor, a filter capacitor and a line equivalent inductor.

[0056] When multiple energy storage converters are operated in parallel without interconnection and off-grid connection (i.e., the grid-connected switch QF is in the disconnected state, multiple energy storage converters are operated in parallel, and each energy storage converter is independent and unconnected in operation control), the current of each energy storage converter cannot be evenly distributed due to the lack of necessary connection in operation control. When the load suddenly increases, the energy storage converter with the largest current output will have an overcurrent fault. Uneven current distribution will affect the stable operation of the parallel system, so the off-grid parallel operation control technology of multiple energy storage converters is particularly important.

[0057] In order to improve the operating stability of a multi-energy storage inverter off-grid parallel system, an embodiment of the present invention discloses a multi-energy storage inverter off-grid parallel operation control method. The method selects one of the multiple energy storage inverters as a host and the rest as slaves, and adopts a control strategy of host as the main and slave as the auxiliary. The host sends a unified control instruction to all slaves (that is, the output of the host's power outer loop and voltage middle loop), and the slaves are controlled according to the unified instruction of the host, so that the entire station is integrated into a whole, and unified and coordinated control of the entire station is realized. At this time, it is easy to realize current equalization control to avoid unstable operation of the parallel system caused by uneven current output.

[0058] For the purpose of reference and clarity, the technical terms, abbreviations or acronyms used below are summarized as follows:

[0059] PWM: Pulse Width Modulation, pulse width modulation;

[0060] Clark Transformation: Clarke Transformation, Clarke Transformation;

[0061] SOC: State Of Charge, remaining power;

[0062] SVPWM: Space Vector Pulse Width Modulation, space vector pulse width modulation;

[0063] PI: Proportional Integral, proportional integral;

[0064] PR:Proportional Resonant,proportional resonance;

[0065] PIR: Proportional Integral Resonant, proportional integral resonance;

[0066] EMS: Energy Management System, power management system.

[0067] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] See also Figure 2 , a method for controlling off-grid parallel operation of multiple energy storage converters disclosed in an embodiment of the present invention specifically includes:

[0069] Step S01: determine one of the multiple energy storage converters in the energy storage power station as a master, and the rest as slaves; then proceed to step S02.

[0070] Specifically, the master and slave machines can be arbitrarily designated manually, or they can be automatically designated by the host computer of the energy storage inverter according to preset rules. The preset rules are, for example: obtaining the SOC (State Of Charge) of each battery pack in the parallel system. When the parallel system is in the battery pack discharge state, the energy storage inverter corresponding to the battery pack with the largest SOC is set as the master, and the rest are slaves; when the parallel system is in the battery pack charging state, the energy storage inverter corresponding to the battery pack with the smallest SOC is set as the master, and the rest are slaves. The host is the core of the entire parallel system. If the host stops working before the slave, the entire parallel system will stop working. The preset rules determine the ownership of the host and the slave according to the SOC of each battery pack, which can ensure that the host is the last to stop working regardless of whether the parallel system is in the battery pack discharge state or charging state.

[0071] Step S02: The host performs three-loop control of the power outer loop, voltage middle loop, and current inner loop according to the load power of the entire station to obtain the host PWM signal; wherein, the host's power outer loop adopts a droop control strategy, and the outputs of the host's power outer loop and voltage middle loop are sent to each slave; then enter step S03.

[0072] Step S03: The control logic of each slave includes: the slave performs three-loop control of the power outer loop, the voltage middle loop and the current inner loop according to the output of the power outer loop and the voltage middle loop of the host to obtain the slave PWM signal; wherein the power outer loop of the slave adopts a droop control strategy, the given value of the voltage middle loop of the slave is the sum of the output of the power outer loop of the host and the first compensation value, the given value of the current inner loop of the slave is the sum of the output of the voltage middle loop of the host and the second compensation value, the first compensation value is calculated based on the output of the power outer loop of this slave, and the second compensation value is calculated based on the output of the voltage middle loop of this slave.

[0073] Specifically, the communication method between the host and the slaves may adopt a bus structure, in which case the host sends instructions to all slaves through the bus in a broadcasting manner, but the present invention is not limited thereto.

[0074] The control principle block diagram of the host is as follows Figure 3 As shown below, combined Figure 1 The host's power outer loop, voltage middle loop, and current inner loop are described in detail respectively.

[0075] 1. Host power outer ring

[0076] The host's power outer loop adopts droop control, that is, the host obtains stable voltage and frequency through QU droop control and PF droop control respectively. Droop control is a well-known automatic control technology used to control the frequency and voltage stability of the power system (in this application, the power system specifically refers to a multi-energy storage inverter off-grid parallel system). In the power system, changes in frequency and voltage will affect the stability and safety of the power system. Therefore, droop control technology is often used to control these variables to ensure stable and safe operation of the power system.

[0077] The power droop control of the host uses the load power of the entire station. At this time, the host performs power outer loop control, which specifically includes the following steps A1 to A2:

[0078] Step A1: The host performs power calculation based on the load three-phase voltage VLabc and the load three-phase current ILabc to obtain the load active power PL and the load reactive power QL. The power calculation formula is as follows:

[0079] PL=VLa×ILa+VLb×ILb+VLc×ILc,

[0080]

[0081] In the formula, VLa, VLb, VLc represent the load A phase voltage, the load B phase voltage and the load C phase voltage respectively, and the load three-phase voltage VLabc includes VLa, VLb and VLc; ILa, ILb and ILc represent the load A phase current, the load B phase current and the load C phase current respectively, and the load three-phase current ILabc includes ILa, ILb and ILc; VLab, VLbc, VLca represent the load AB line voltage, the load BC line voltage and the load CA line voltage respectively; the line voltage is also called the phase-to-phase voltage, for example, the AB line voltage refers to the AB phase voltage, that is, the voltage between phase A and phase B.

[0082] Step A2: The host calculates its own voltage angular frequency ω and voltage given value U, and performs an integral operation on the voltage angular frequency ω ( Figure 3 The voltage phase angle given value θ of the host is obtained by using 1 / S to represent the integral link; the calculation formula is as follows:

[0083] ω=(Pref-PL)×mp+ω o ,

[0084] U=(Qref-QL)×mq+U o ;

[0085] Where Pref represents the total active power given value of the whole station issued by EMS, Qref represents the total reactive power given value of the whole station issued by EMS, mp represents the host active power droop coefficient, mq represents the host reactive power droop coefficient, ω o Indicates the rated angular frequency, U o Indicates rated voltage.

[0086] The host's voltage given value U and voltage phase angle given value θ are the output of the host's power outer loop. The output of the host's power outer loop is the given value of the host's voltage middle loop and is sent to all slaves through communication.

[0087] 2. Voltage Central Ring of Host

[0088] The host performs voltage mid-loop control, which specifically includes the following steps B1 to B2:

[0089] Step B1: The host performs voltage command calculation based on the voltage given value U and the voltage phase angle given value θ to obtain the host's α-axis voltage given value U×sinθ and β-axis voltage given value U×cosθ; and the host performs Clark transformation on its own three-phase voltage V to obtain the host's α-axis voltage feedback value U 1α and β-axis voltage feedback value U 1β ;

[0090] Specifically, Clark transformation is a transformation that converts three-phase alternating current into two-phase alternating current. The Clark transformation formula is as follows:

[0091]

[0092] Step B2: The host compares the α-axis voltage given value U×sinθ with the α-axis voltage feedback value U 1α The difference is input into the host voltage loop controller to obtain the α-axis voltage U output by the host voltage loop controller 1α * ; The β-axis voltage given value U×cosθ and the β-axis voltage feedback value U 1β The difference is input into the host voltage loop controller to obtain the β-axis voltage U output by the host voltage loop controller 1β * .U 1α * and U 1β * The output of the host voltage mid-loop is the given value of the host current inner loop and is transmitted to each slave through communication.

[0093] 3. Current Inner Loop

[0094] The host performs current inner loop control, which specifically includes: the host performs Clark transformation on its own three-phase current I to obtain the host α-axis current feedback value I 1α and the host β-axis current feedback value I 1β , the α-axis voltage U 1α * and the α-axis current feedback value I 1α The difference is input into the host current loop controller to obtain the α-axis current signal I output by the host current loop controller 1α * , the β-axis voltage U 1β * and the β-axis current feedback value I 1β The difference is input into the host current loop controller to obtain the β-axis current I output by the host current loop controller 1β * . α-axis current signal I 1α * and β-axis current I 1β * It is the output of the host's current inner loop.

[0095] After that, the host can use the α-axis current signal I 1α * and β-axis current I 1β * A PWM controller (eg, an SVPWM controller) is controlled to generate a PWM wave of the host to control a power unit of the host.

[0096] In addition, traditional voltage loop controllers and current loop controllers mostly use PI controllers. The voltage loops are all AC signals, but PI control cannot achieve zero-error tracking of AC signals and has poor anti-interference ability. The PR controller can provide high gain at the resonant frequency point to achieve zero-error tracking control of the voltage command, so the voltage loop controller is recommended to use a PR controller. Most of the current of the energy storage converter is also an AC signal, but due to various reasons, a certain amount of DC will inevitably be generated. The DC component in the energy storage converter will cause serious damage to the power grid equipment, causing DC bias of the transformer and magnetic saturation of the transformer. Therefore, the national standards for energy storage converters and inverters have restricted the DC component. The DC value in the current loop is basically zero. In order to suppress the DC current component, the embodiment of the present invention recommends adding integral control on the basis of PR control in the current loop. Integral control can eliminate the DC static error, so the current loop control adopts PIR control. Figure 3 In the example, the host voltage loop controller is a PR controller and the host current loop controller is a PIR controller.

[0097] The control principles of slaves 1 to n are the same, where n is the total number of slaves. The control principle block diagram of slave 1 is as follows: Figure 4 As shown below, combined Figure 1 The power outer loop, voltage middle loop and current inner loop of slave 1 are described in detail respectively.

[0098] 1. Power outer loop of slave 1

[0099] The power outer loop of slave 1 also adopts droop control. Slave 1 performs power outer loop control, which specifically includes the following steps D1 to D2:

[0100] Step D1: slave 1 performs power calculation based on its own three-phase voltage V2abc and three-phase current I2abc to obtain active power P2 and reactive power Q2 of slave 1;

[0101] Step D2: Slave 1 calculates its own voltage angular frequency ω2 and voltage reference value U2 * , and integrate the voltage angular frequency ω2 to obtain the voltage phase angle given value θ2 * ; The calculation formula is as follows:

[0102] ω2=(P2ref-P2)×mp2+ω o ,

[0103] U2 * =(Q2ref-QL)×mq2+U o ;

[0104] Where P2ref represents the active power given value of slave 1 sent by EMS, Q2ref represents the reactive power given value of slave 1 sent by EMS, mp2 represents the active power droop coefficient of slave 1, mq2 represents the reactive power droop coefficient of slave 1, ω o Indicates the rated angular frequency, U o Indicates rated voltage.

[0105] Voltage reference value U2 of slave 1 * And the voltage phase angle given value θ2 * is the output of the power outer loop of slave 1, and the output of the power outer loop of slave 1 is the given value of the voltage middle loop of slave 1.

[0106] 2. Voltage Central Ring of Slave 1

[0107] Slave 1 performs voltage mid-loop control, specifically including the following steps E1 to E2:

[0108] Step E1: Slave 1 calculates its own voltage given value U2 and phase angle given value θ2.

[0109] Specifically, the calculation of the final voltage given value U2 and phase angle given value θ2 of slave 1 is mainly based on the host and supplemented by slave 1, that is, the voltage given value U and voltage phase angle given value θ of the host are mainly used, and the voltage given value U2 calculated by slave 1 itself is * and phase angle given value θ2 * It only plays a compensatory role, used to compensate for the sampling error between the host and slave 1, and enhance the robustness of the system; the voltage setting value of slave 1 U2 = m2 × U2 * +m1×U, phase angle given value θ2=m2×θ2 * +m1×θ, m1 and m2 are both constants.

[0110] Step E2: Slave 1 calculates the voltage command according to the voltage given value U2 and the phase angle given value θ2, and obtains the α-axis voltage given value U2×sinθ2 and the β-axis voltage given value U2×cosθ2 of slave 1; and slave 1 performs Clark transformation on its own three-phase voltage V2abc to obtain the α-axis voltage feedback value U 2α and the β-axis voltage feedback value U of slave 1 2β ;

[0111] Step E3: Slave 1 converts the α-axis voltage given value U2×sinθ2 and the α-axis voltage feedback value U 2α The difference is input into the voltage loop controller of slave 1, and the α-axis voltage U output by the voltage loop controller of slave 1 is obtained. 2α * ; The β-axis voltage given value U2×cosθ2 and the β-axis voltage feedback value U 2βThe difference is input into the voltage loop controller of slave 1, and the β-axis voltage U output by the voltage loop controller of slave 1 is obtained. 2β * .U 2α * and U 2β * As the output value of the slave 1 voltage middle loop, the output value of the slave 1 voltage middle loop is the given value of the slave 1 current inner loop.

[0112] 3. Current inner loop of slave 1

[0113] Slave 1 performs current inner loop control, which specifically includes the following steps F1 to F2:

[0114] Step F1: Slave 1 calculates its own α-axis current loop given value I 2αref and the β-axis current loop given value I 2βref ;I 2αref =k3×U 1α * +k2×U 2α * , I 2βref =k3×U 1β * +k2×U 2β * ; k3 and k2 are both constants. 2αref and I 2βref The calculation is based on the host computer U 1α * and U 1β * U calculated by the master and slave 1 2α * and U 2β * It plays the role of auxiliary control, compensates for the sampling errors of the master and slave machines, and enhances the robustness of the system.

[0115] Optionally, considering that the delay in the master-slave communication is inevitable, there will be a control cycle delay no matter how fast the communication speed is, and the communication delay will also introduce phase lag, resulting in limited control loop bandwidth, reduced phase margin, and unstable energy storage converter control system. Therefore, in order to improve the stability and control performance of the energy storage converter, it is necessary to reduce the impact of communication delay and add a phase advance compensation link. The phase advance compensation transfer function is: k1 is the proportional gain coefficient, and T is the integral time constant. Specifically, the slave receives the voltage loop output U from the host. 1α * , U 1β * , through the phase lead compensation function, plus the slave voltage loop output U 2α* , U 2β * Multiply by k2, the α-axis current loop given value of slave 1 β-axis current loop set value of slave 1 By adding a phase advance compensation link, the impact of communication delay can be reduced and the system robustness and stability can be further enhanced.

[0116] Step F2: Slave 1 performs Clark transformation on its own three-phase current I2abc to obtain the α-axis current feedback value I of slave 1 2α and the β-axis current feedback value I 2β The α-axis current loop given value I of slave 1 2αref and the α-axis current feedback value I 2α The difference is input into the current loop controller of slave 1 to obtain the α-axis current signal I output by the current loop controller of slave 1. 2α * , set the β-axis voltage of slave 1 to I 2βref and the β-axis current feedback value I 2β The difference is input into the current loop controller of slave 1 to obtain the β-axis current I output by the current loop controller of slave 1. 2β * . α-axis current signal I 2α * and β-axis current I 2β * It is the output of the current inner loop of slave 1.

[0117] Afterwards, slave 1 generates the α-axis current signal I 2α * and β-axis current I 2β * Controlling a PWM controller (such as an SVPWM controller) to generate a PWM wave of slave 1 to control the power unit of slave 1, Figure 4 In the example, the PWM wave generated by slave 1 is recorded as PWM2.

[0118] Optionally, the voltage loop of slave 1 adopts a PR controller and the current loop adopts a PIR controller. The reason is the same as that of the master and will not be repeated here. Since the power outer loop adjustment speed is relatively slow, the communication delay effect is very small and can be ignored, and there is no need to consider adding phase advance compensation control.

[0119] In addition, corresponding to the above-mentioned method embodiments, an embodiment of the present invention also discloses a multi-energy storage inverter off-grid parallel operation control device, including: a processor and a memory, the memory stores a program, and when the program is executed by the processor, it implements any of the above-mentioned multi-energy storage inverter off-grid parallel operation control methods.

[0120] Another embodiment of the present application further provides a computer-readable storage medium, which stores instructions, and when the computer-readable storage medium is executed on a computer or a processor, the computer or the processor executes any of the above-mentioned off-grid parallel operation control methods for multiple energy storage inverters.

[0121] The computer-readable storage medium may be a non-temporary computer-readable storage medium, for example, the non-temporary computer-readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, etc.

[0122] Another embodiment of the present application further provides a computer program product, which, when executed on an electronic device, is used to execute any of the above-mentioned off-grid parallel operation control methods for multiple energy storage inverters.

[0123] In the embodiments of the present invention, "one or more" means one, two or more than two; "and / or" describes the association relationship of associated objects, indicating that three relationships may exist; for example, A and / or B may mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B may be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0124] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the embodiments of the present invention. Therefore, the embodiments of the present invention will not be limited to the embodiments shown herein, but rather to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling off-grid parallel operation of multiple energy storage converters, characterized in that: include: Determine one of the multiple energy storage converters in the energy storage power station as the master, and the others as slaves; The host performs three-loop control of the power outer loop, voltage middle loop, and current inner loop according to the load power of the entire station to obtain the host PWM signal; the host's power outer loop adopts a droop control strategy, and the outputs of the host's power outer loop and voltage middle loop are sent to each slave; The slave performs three-loop control of the power outer loop, the voltage middle loop, and the current inner loop according to the output of the power outer loop and the voltage middle loop of the host to obtain the slave PWM signal; wherein the power outer loop of the slave adopts a droop control strategy, the given value of the voltage middle loop of the slave is the sum of the output of the power outer loop of the host and the first compensation value, and the given value of the current inner loop of the slave is the sum of the output of the voltage middle loop of the host and the second compensation value, the first compensation value is calculated based on the output of the power outer loop of the slave, and the second compensation value is calculated based on the output of the voltage middle loop of the slave; Among them, the host performs power outer loop control, including: The host performs power calculation based on the load three-phase voltage and load three-phase current to obtain the load active power PL and load reactive power QL; the host calculates its own voltage angular frequency ω and voltage set value U, and integrates the voltage angular frequency ω to obtain the host's voltage phase angle set value θ; the host's voltage set value U and voltage phase angle set value θ are the outputs of the host's power outer loop and are sent to each slave; the calculation formulas for the voltage phase angle set value θ and the voltage set value U are as follows: ω=(Pref-PL)×mp+ω o , U=(Qref-QL)×mq+U o ; Where Pref represents the total active power given value of the entire station issued by the energy management system EMS of the energy storage power station, Qref represents the total reactive power given value of the entire station issued by EMS, mp represents the active droop coefficient, mq represents the reactive droop coefficient, ω o Indicates the rated angular frequency, U o Indicates rated voltage; Among them, the host performs voltage mid-loop control, including: The host calculates the voltage command according to the voltage given value U and the voltage phase angle given value θ, and obtains the host's α-axis voltage given value U×sinθ and β-axis voltage given value U×cosθ; and the host performs Clark transformation on its own three-phase voltage V to obtain the host's α-axis voltage feedback value U 1α and β-axis voltage feedback value U 1β ; The host converts the α-axis voltage given value U×sinθ and the α-axis voltage feedback value U 1α The difference is input into the host voltage loop controller to obtain the α-axis voltage U output by the host voltage loop controller 1α * ; The β-axis voltage given value U×cosθ and the β-axis voltage feedback value U 1β The difference is input into the host voltage loop controller to obtain the β-axis voltage U output by the host voltage loop controller 1β * ; α axis voltage U 1α * and β-axis voltage U 1β * It is the output of the voltage loop of the host and is sent to each slave; Among them, the host performs current inner loop control, including: The host performs Clark transformation on its own three-phase current I to obtain the host α-axis current feedback value I 1α and the host β-axis current feedback value I 1β ; The host will α axis voltage U 1α * and the α-axis current feedback value I 1α The difference is input into the host current loop controller to obtain the α-axis current signal I output by the host current loop controller 1α * ; Set the β axis voltage U 1β * and the β-axis current feedback value I 1β The difference is input into the host current loop controller to obtain the β-axis current I output by the host current loop controller 1β * ;α-axis current signal I 1α * and β-axis current I 1β * It is the output of the host's current inner loop, used to control the PWM controller to generate the host's PWM wave; The control logic of each slave is the same. Slave 1 is one of the slaves. Slave 1 performs power outer loop control, including: Slave 1 calculates power based on its own three-phase voltage V2abc and three-phase current I2abc to obtain active power P2 and reactive power Q2 of slave 1; slave 1 calculates its own voltage angular frequency ω2 and voltage given value U2 * , and integrate the voltage angular frequency ω2 to obtain the voltage phase angle given value θ2 * ; Voltage setting value U2 of slave 1 * And the voltage phase angle given value θ2 * is the output of the power outer loop of slave 1; where the voltage angular frequency ω2 and the voltage given value U2 * The calculation formula is as follows: ω2=(P2ref-P2)×mp2+ω o , U2 * =(Q2ref-QL)×mq2+U o ; Where P2ref represents the active power given value of slave 1 sent by EMS, Q2ref represents the reactive power given value of slave 1 sent by EMS, mp2 represents the active power droop coefficient of slave 1, mq2 represents the reactive power droop coefficient of slave 1, ω o Indicates the rated angular frequency, U o Indicates rated voltage; Among them, slave 1 performs voltage mid-loop control, including: Slave 1 calculates its own voltage given value U2 and phase angle given value θ2; U2 = m2 × U2 * +m1×U,θ2=m2×θ2 * +m1×θ; m1 and m2 are both constants; Slave 1 calculates the voltage command according to the voltage given value U2 and the phase angle given value θ2, and obtains the α-axis voltage given value U2×sinθ2 and the β-axis voltage given value U2×cosθ2 of slave 1; and slave 1 performs Clark transformation on its own three-phase voltage V2abc to obtain the α-axis voltage feedback value U of slave 1. 2α and the β-axis voltage feedback value U of slave 1 2β ; Slave 1 converts the α-axis voltage given value U2×sinθ2 into the α-axis voltage feedback value U 2α The difference is input into the voltage loop controller of slave 1, and the α-axis voltage U output by the voltage loop controller of slave 1 is obtained. 2α * ; The β-axis voltage given value U2×cosθ2 and the β-axis voltage feedback value U 2β The difference is input into the voltage loop controller of slave 1, and the β-axis voltage U output by the voltage loop controller of slave 1 is obtained. 2β * ; U 2α * and U 2β * As the output value of the middle loop of the voltage of slave 1, the output value of the middle loop of the voltage of slave 1 is the given value of the inner loop of the current of slave 1; Among them, slave 1 performs current inner loop control, including: Slave 1 calculates its own α-axis current loop given value I 2αref and the β-axis current loop given value I 2βref , and its calculation formula is as follows: In the formula, k2 is a constant, k1 is a proportional gain coefficient, and T is an integral time constant; Slave 1 performs Clark transformation on its own three-phase current I2abc to obtain the α-axis current feedback value I of slave 1 2α and the β-axis current feedback value I 2β The α-axis current loop given value I of slave 1 2αref and the α-axis current feedback value I 2α The difference is input into the current loop controller of slave 1 to obtain the α-axis current signal I output by the current loop controller of slave 1. 2α * , set the β-axis voltage of slave 1 to I 2βref and the β-axis current feedback value I 2β The difference is input into the current loop controller of slave 1 to obtain the β-axis current I output by the current loop controller of slave 1. 2β * ;α-axis current signal I 2α * and β-axis current I 2β * It is the output of the current inner loop of slave 1 and is used to control the PWM controller to generate the PWM wave of slave 1.

2. The off-grid parallel operation control method of multiple energy storage converters according to claim 1, characterized in that: The step of determining one of the multiple energy storage converters as a master and the others as slaves includes: Obtain the remaining power SOC of the battery pack connected to each energy storage converter respectively; When each battery pack is in a discharging state, the energy storage converter corresponding to the battery pack with the largest SOC is set as the master, and the others are set as slaves; When each battery pack is in a charging state, the energy storage converter corresponding to the battery pack with the smallest SOC is set as the master, and the others are set as slaves.

3. The off-grid parallel operation control method of multiple energy storage converters according to claim 1, characterized in that: The host voltage loop controller and the slave 1 voltage loop controller are both proportional resonant controllers, and the host current loop controller and the slave 1 current loop controller are both proportional integral resonant controllers.

4. A multi-energy storage converter off-grid parallel operation control device, characterized in that: include: A processor and a memory, wherein a program is stored in the memory, and when the program is executed by the processor, the off-grid parallel operation control method of multiple energy storage converters as described in any one of claims 1 to 3 is implemented.

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