阅读说明：本技术 一种锂电池储能型mmc的等效仿真方法 (Equivalent simulation method for energy storage type MMC of lithium battery ) 是由 周原冰 肖晋宇 侯金鸣 刘耀 吴佳玮 赵小令 徐政 张哲任 徐雨哲 于 2019-09-20 设计创作，主要内容包括：本发明公开了一种锂电池储能型MMC的等效仿真方法,包括：(1)获取MMC运行参数；(2)根据MMC运行参数,构建MMC各桥臂等效电路并确定桥臂等效电路中各等效元件的参数；(3)根据桥臂等效电路建立MMC仿真模型,基于桥臂中子模块t时刻的电气量对该模型进行仿真计算,得到外电路t+Δt时刻的电气量；(4)根据外电路t+Δt时刻的电气量计算出桥臂中各子模块t+Δt时刻的电气量。本发明填补了目前锂电池储能型MMC等效仿真建模的空白,能为未来工程设计提供一定的参考,通用性强,理论上该等效仿真方法不但适用于桥臂中全部子模块都正常运行或全部子模块都闭锁的情况,也适用于桥臂中部分子模块闭锁的情况。(The invention discloses an equivalent simulation method of a lithium battery energy storage type MMC, which comprises the following steps: (1) obtaining MMC operation parameters; (2) according to the MMC operation parameters, constructing each bridge arm equivalent circuit of the MMC and determining the parameters of each equivalent element in the bridge arm equivalent circuit; (3) establishing an MMC simulation model according to the bridge arm equivalent circuit, and carrying out simulation calculation on the model based on the electric quantity at the t moment of a neutron module in the bridge arm to obtain the electric quantity at the t + delta t moment of an external circuit; (4) and calculating the electric quantity of each submodule at the time of t + delta t in the bridge arm according to the electric quantity of the external circuit at the time of t + delta t. The invention fills the blank of the equivalent simulation modeling of the energy storage type MMC of the lithium battery at present, can provide a certain reference for future engineering design, has strong universality, and is theoretically suitable for the condition that all the submodules in a bridge arm normally run or all the submodules are locked as well as the condition that some submodules in the bridge arm are locked.)

1. An equivalent simulation method of a lithium battery energy storage type MMC is characterized in that the MMC is of a three-phase six-bridge arm structure, and each bridge arm is formed by cascading a bridge arm reactance and a plurality of energy storage type sub-modules; the equivalent simulation method comprises the following steps:

(1) obtaining MMC operation parameters;

(2) constructing an equivalent circuit of each bridge arm of the MMC according to the MMC operating parameters, and determining the parameters of each equivalent element in the bridge arm equivalent circuit;

(3) establishing a simulation model of the MMC according to the bridge arm equivalent circuit, and carrying out simulation calculation on the model based on the electric quantity of each submodule at the time t for any bridge arm of the MMC to obtain bridge arm current i at the time t + delta t_arm(t + Δ t) and a blocking current i_csm(t + Δ t), wherein t is a natural number and Δ t is a simulation step length;

(4) bridge arm current i according to t + delta t moment_arm(t + Δ t) and a blocking current i_csmAnd (t + delta t) calculating the electric quantity of each submodule at the time of t + delta t in the bridge arm.

2. The equivalent simulation method according to claim 1, wherein: the MMC operation parameters comprise bridge arm currents of the MMC and switch states of submodules.

3. The equivalent simulation method according to claim 1, wherein: the energy storage type submodule comprises four IGBT tubes T with anti-parallel diodes₁～T₄A capacitor C₀An inductor L₁And an energy storage lithium battery; wherein, IGBT tube T₁Collector and capacitor C₀Positive electrode and IGBT tube T₃Is connected with the collector of the IGBT tube T₁Emitter and IGBT tube T₂And the collector of (A) is connected with and used as the anode of the submodule, the IGBT tube T₂Emitter and capacitor C₀Negative electrode of (1), IGBT tube T₄The emitting electrode and the negative electrode of the energy storage lithium battery are connected and used as the negative electrode of the sub-module, and the IGBT tube T₃Emitter and IGBT tube T₄Collector and inductor L₁Is connected to one end of an inductor L₁The other end of the four IGBT tubes T is connected with the anode of the energy storage lithium battery₁～T₄The base of each of the first and second switches receives a switching signal provided by an external control device.

4. The equivalent simulation method according to claim 3, wherein: the equivalent circuit of the energy storage lithium battery is a first-order RC circuit which is composed of an ideal voltage source U_bat0Two resistors R_bat0～R_bat1And a capacitor C_bat0Composition is carried out; wherein, the capacitor C_bat0Negative electrode and resistor R_bat0One end of the capacitor C is connected with the positive electrode of the lithium battery_bat0Positive electrode and resistor R_bat0And the other end of (3) and a resistor R_bat1Is connected to one end of a resistor R_bat1And the other end of the same and an ideal voltage source U_bat0Connected to the positive pole of the ideal voltage source U_bat0As a negative electrode of a lithium battery.

5. The equivalent simulation method according to claim 4, wherein: for any bridge arm of the MMC, the equivalent circuit of the MMC is composed of three equivalent resistors R_eq1～R_eq3Two equivalent voltage sources U_eq1～U_eq2And two equivalent diodes D_eq1～D_eq2Forming; wherein, the equivalent voltage source U_eq1The anode of the bridge arm equivalent circuit is used as the anode of the bridge arm equivalent circuit, and the equivalent voltage source U_eq1And the equivalent resistance R_eq1Is connected to one end of an equivalent resistor R_eq1And the other end of the same diode D_eq1Anode of (2), equivalent diode D_eq2And the equivalent resistance R_eq3Is connected to an equivalent diode D_eq1Cathode and equivalent voltage source U of_eq2Is connected with the anode of the equivalent voltage source U_eq2And the equivalent resistance R_eq2Is connected to one end of an equivalent resistor R_eq2And the other end of the same diode D_eq2Anode and equivalent resistance R_eq3The other end of the bridge arm is connected with the other end of the bridge arm to be used as a negative electrode of the bridge arm equivalent circuit.

6. The equivalent simulation method according to claim 5, wherein: for any bridge arm of the MMC, calculating and determining the parameters of each equivalent element in the equivalent circuit of the bridge arm by the following formula;

R_{temp1_j}(t)＝R_{Cbat0_j}(t)·R_{bat0_j}(t)/[R_{Cbat0_j}(t)+R_{bat0_j}(t)]+R_{bat1_j}(t)+R_{L1_j}(t)

R_{temp2_j}(t)＝R_{4_j}(t)·R_{temp1_j}(t)/[R_{4_j}(t)+R_{temp1_j}(t)]+R_{3_j}(t)

R_{temp3_j}(t)＝R_{C0_j}(t)·R_{temp2_j}(t)/[R_{C0_j}(t)+R_{temp2_j}(t)]

U_{temp1_j}(t)＝-U_{ceq1_j}(t)·R_{bat0_j}(t)/[R_{Cbat0_j}(t)+R_{bat0_j}(t)]+U_{bat0_j}(t)+U_{leq1_j}(t)

U_{temp2_j}(t)＝U_{temp1_j}(t)·R_{4_j}(t)/[R_{4_j}(t)+R_{temp1_j}(t)]

U_{temp3_j}(t)＝[U_{temp2_j}(t)·R_{C0_j}(t)+U_{ceq0_j}(t)·R_{temp2_j}(t)]/[R_{C0_j}(t)+R_{temp2_j}(t)]

U_{ceq0_j}(t)＝U_{C0_j}(t)+R_{C0_j}(t)·i_{C0_j}(t)

U_{ceq1_j}(t)＝U_{Cbat0_j}(t)+R_{Cbat0_j}(t)·i_{Cbat0_j}(t)

U_{leq1_j}(t)＝U_{L1_j}(t)+R_{L1_j}(t)·i_{L1_j}(t)

R_{bat0_j}(t)＝r_bat0R_{bat1_j}(t)＝r_bat1U_{bat0_j}(t)＝u_bat0

wherein: u shape_eq1(t) represents the equivalent voltage source U at time t_eq1Voltage value of U_eq2(t) represents time t or the likeEffective voltage source U_eq2Voltage value of R_eq1(t) represents the equivalent resistance R at time t_eq1Resistance value of R_eq2(t) represents the equivalent resistance R at time t_eq2Resistance value of R_eq3(t) represents the equivalent resistance R at time t_eq3A represents the set formed by all the sub-modules in the locking state in the current bridge arm, B represents the set formed by all the sub-modules in the normal operation state in the current bridge arm, j represents any sub-module in the bridge arm, R_{C0_j}(t)、R_{Cbat0_j}(t) and R_{L1_j}(t) respectively representing capacitors C in the bridge arm submodule j at the moment of t₀Lithium battery capacitor C_bat0And an inductance L₁Equivalent resistance value of R_{1_j}(t)～R_{4_j}(T) respectively representing IGBT tubes T in bridge arm submodule j at time T₁～T₄Equivalent resistance value of U_{C0_j}(t)、U_{Cbat0_j}(t) and U_{L1_j}(t) respectively representing capacitors C in the bridge arm submodule j at the moment of t₀Lithium battery capacitor C_bat0And an inductance L₁Voltage of i_{C0_j}(t)、i_{Cbat0_j}(t) and i_{L1_j}(t) respectively representing capacitors C in the bridge arm submodule j at the moment of t₀Lithium battery capacitor C_bat0And an inductance L₁C is a current of₀For the capacitance C in the submodule₀Capacity of c_bat0For the capacitor C of the lithium battery in the submodule_bat0Capacity value of l₁For the inductance L in the submodule₁Sensitivity value of r_bat0And r_bat1Respectively, the resistance R of the lithium battery in the submodule_bat0And R_bat1Resistance value of u_bat0For ideal voltage source U of lithium battery in submodule_bat0The remaining variables are intermediate variables.

7. The equivalent simulation method according to claim 6, wherein: for any bridge arm of the MMC, calculating the electric quantity of each submodule at the t + delta t moment in the bridge arm by the following formula;

i_{C0_j}(t+Δt)＝[i_{csm_j}(t+Δt)·R_{temp2_j}(t+Δt)+U_{temp2_j}(t+Δt)-U_{ceq0_j}(t)]/[R_{temp2_j}(t+Δt)+R_{C0_j}(t+Δt)]

U_{C0_j}(t+Δt)＝U_{ceq0_j}(t)+R_{C0_j}(t+Δt)·i_{C0_j}(t+Δt)

U_{L1_j}(t+Δt)＝R_{L1_j}(t+Δt)·i_{L1_j}(t+Δt)-U_{leq1_j}(t)

i_{Cbat0_j}(t+Δt)＝[i_{L1_j}(t+Δt)·R_{bat0_j}(t+Δt)-U_{ceq1_j}(t)]/[R_{bat0_j}(t+Δt)+R_{Cbat0_j}(t+Δt)]

U_{Cbat0_j}(t+Δt)＝U_{ceq1_j}(t)+R_{Cbat0_j}(t+Δt)·i_{Cbat0_j}(t+Δt)

R_{temp2_j}(t+Δt)＝R_{4_j}(t+Δt)·R_{temp1_j}(t)/[R_{4_j}(t+Δt)+R_{temp1_j}(t)]+R_{3_j}(t+Δt)

U_{temp2_j}(t+Δt)＝U_{temp1_j}(t)·R_{4_j}(t+Δt)/[R_{4_j}(t+Δt)+R_{temp1_j}(t)]

R_{temp3_j}(t+Δt)＝R_{C0_j}(t+Δt)·R_{temp2_j}(t+Δt)/[R_{C0_j}(t+Δt)+R_{temp2_j}(t+Δt)]

U_{temp3_j}(t+Δt)＝[U_{temp2_j}(t+Δt)·R_{C0_j}(t+Δt)+U_{ceq0_j}(t)·R_{temp2_j}(t+Δt)]/[R_{C0_j}(t+Δt)+R_{temp2_j}(t+Δt)]

R_{bat0_j}(t+Δt)＝r_bat0R_{bat1_j}(t+Δt)＝r_bat1

wherein: u shape_{C0_j}(t+Δt)、U_{Cbat0_j}(t + Δ t) and U_{L1_j}(t + delta t) respectively represents the capacitor C in the bridge arm submodule j at the moment of t + delta t₀Lithium battery capacitor C_bat0And an inductance L₁Voltage of i_{C0_j}(t+Δt)、i_{Cbat0_j}(t + Δ t) and i_{L1_j}(t + delta t) respectively represents the capacitor C in the bridge arm submodule j at the moment of t + delta t₀Lithium battery capacitor C_bat0And an inductance L₁Current of R_{C0_j}(t+Δt)、R_{Cbat0_j}(t + Δ t) and R_{L1_j}(t + delta t) respectively represents the capacitor C in the bridge arm submodule j at the moment of t + delta t₀Lithium battery capacitor C_bat0And an inductance L₁Equivalent resistance value of R_{1_j}(t+Δt)～R_{4_j}(T + delta T) respectively represents IGBT tube T in bridge arm submodule j at the moment of T + delta T₁～T₄The other variables are intermediate variables.

8. The equivalent simulation method according to claim 5, wherein: the latching current i_csm(t + delta t) is equivalent resistance R in the bridge arm equivalent circuit at the moment of t + delta t_eq2The current of (2).

Technical Field

The invention belongs to the technical field of power transmission and distribution of a power system, and particularly relates to an equivalent simulation method of a lithium battery energy storage type MMC.

Background

Energy resources and energy requirements in China are in a reverse distribution pattern, energy resource allocation needs to be optimized nationwide, and the high-voltage direct-current transmission technology is an important technical means for realizing long-distance large-capacity transmission. Up to now, the flexible dc power transmission technology based on Modular Multilevel Converter (MMC) has the most application prospect.

The existing theoretical research and engineering practice show that the alternating current system and the direct current system in the alternating current-direct current interconnected power grid have strong mutual influence and are mainly reflected in the following three aspects:

1. a transmitting ac fault may affect a receiving ac system through a dc system. When the bus voltage of the sending-end converter station drops seriously due to a fault, the capacity of the sending-end converter station for absorbing active power from the alternating current system is limited, which means that the power injected into the system by the receiving-end converter station is reduced instantaneously, and then disturbance is generated on the receiving-end alternating current system.

2. The receiving end alternating current fault can affect the transmitting end alternating current system through the direct current system. For a receiving-end MMC converter station, when the bus voltage of the receiving-end converter station drops seriously due to a fault, the active power of the receiving-end converter station is blocked, the instantaneous high power surplus of a direct-current system occurs, the direct-current side generates serious overvoltage, and then the locking of the receiving-end MMC converter station is triggered, the active power of a sending-end power grid cannot be sent out, and finally the transient frequency of the sending-end power grid rises.

3. A dc fault may affect the proper operation of an ac system. On one hand, before large-scale commercial application of the high-voltage direct-current circuit breaker, the direct-current system usually adopts a mode of tripping the alternating-current circuit breaker and locking a converter to process direct-current faults, and during the process, power exchange between the direct-current system and the alternating-current system is completely interrupted, so that adverse effects are generated on the stability of the alternating-current system; on the other hand, even if the converter locking problem can be solved through the high-voltage direct-current circuit breaker, for some direct-current systems with special network structures, the breaking of a fault direct-current line can still cause the interruption of direct-current power of some converter stations, and the disturbance of an alternating-current system is caused.

Therefore, active power coupling exists between an alternating current system and a direct current system in the alternating current-direct current interconnected power grid, the direct current system cannot completely cut off mutual transmission of faults between the alternating current-direct current system, and therefore certain potential safety hazards still exist in the alternating current-direct current interconnected power grid. In order to achieve the effect of independent decoupling operation of the direct current system, fully exert the firewall function of the direct current system, and reduce the dependence of the direct current system on the power support of the alternating current system, it is necessary to research a high-voltage direct current power transmission system with short-time power support capability.

At present, the problem that the existing high-voltage direct-current transmission project cannot be independently decoupled and operated is hopefully solved by adding the energy storage device in the high-voltage direct-current transmission system, and the scheme with a better application prospect by adopting the lithium battery as the energy storage device is provided. Considering that the MMC applied to the high-voltage power transmission occasion contains a large number of power electronic devices and can put high requirements on simulation calculation, it is necessary to provide an equivalent simulation method of the lithium battery energy storage type MMC.

Disclosure of Invention

In view of the above, the invention provides an equivalent simulation method for a lithium battery energy storage type MMC, which is simple to implement, strong in applicability and higher in use value in engineering design.

An equivalent simulation method of a lithium battery energy storage type MMC is characterized in that the MMC is of a three-phase six-bridge arm structure, and each bridge arm is formed by cascading a bridge arm reactance and a plurality of energy storage type sub-modules; the equivalent simulation method comprises the following steps:

(1) obtaining MMC operation parameters;

(2) constructing an equivalent circuit of each bridge arm of the MMC according to the MMC operating parameters, and determining the parameters of each equivalent element in the bridge arm equivalent circuit;

(3) establishing a simulation model of the MMC according to the bridge arm equivalent circuit, and carrying out simulation calculation on the model based on the electric quantity of each submodule at the time t for any bridge arm of the MMC to obtain bridge arm current i at the time t + delta t_arm(t + Δ t) and a blocking current i_csm(t + Δ t), wherein t is a natural number and Δ t is a simulation step length;

(4) bridge arm current i according to t + delta t moment_arm(t + Δ t) and a blocking current i_csmAnd (t + delta t) calculating the electric quantity of each submodule at the time of t + delta t in the bridge arm.

Further, the MMC operating parameters include bridge arm currents of the MMC and a switch state in each submodule.

Further, the energy storage type submodule comprises four IGBT tubes T with anti-parallel diodes₁～T₄A capacitor C₀An inductor L₁And an energy storage lithium battery; wherein, IGBT tube T₁Collector and capacitor C₀Positive electrode and IGBT tube T₃Is connected with the collector of the IGBT tube T₁Emitter and IGBT tube T₂And the collector of (A) is connected with and used as the anode of the submodule, the IGBT tube T₂Emitter and capacitor C₀Negative electrode of (1), IGBT tube T₄The emitting electrode and the negative electrode of the energy storage lithium battery are connected and used as the negative electrode of the sub-module, and the IGBT tube T₃Emitter and IGBT tube T₄Collector and inductor L₁Is connected to one end of an inductor L₁The other end of the four IGBT tubes T is connected with the anode of the energy storage lithium battery₁～T₄The base of each of the first and second switches receives a switching signal provided by an external control device.

Furthermore, the equivalent circuit of the energy storage lithium battery is a first-order RC circuit which is composed of an ideal voltage source U_bat0Two resistors R_bat0～R_bat1And a capacitor C_bat0Composition is carried out; wherein, the capacitor C_bat0Negative electrode and resistor R_bat0One end of the capacitor C is connected with the positive electrode of the lithium battery_bat0Positive electrode and resistor R_bat0And the other end of (3) and a resistor R_bat1Is connected to one end of a resistor R_bat1And the other end of the same and an ideal voltage source U_bat0Connected to the positive pole of the ideal voltage source U_bat0As a negative electrode of a lithium battery.

Further, for any bridge arm of the MMC, the equivalent circuit of the MMC is composed of three equivalent resistors R_eq1～R_eq3Two equivalent voltage sources U_eq1～U_eq2And two equivalent diodes D_eq1～D_eq2Forming; wherein, the equivalent voltage source U_eq1The anode of the bridge arm equivalent circuit is used as the anode of the bridge arm equivalent circuit, and the equivalent voltage source U_eq1And the equivalent resistance R_eq1Is connected to one end of an equivalent resistor R_eq1And the other end of the same diode D_eq1Anode of (2), equivalent diode D_eq2And the equivalent resistance R_eq3Is connected to an equivalent diode D_eq1Cathode and equivalent voltage source U of_eq2Is connected with the anode of the equivalent voltage source U_eq2And the equivalent resistance R_eq2Is connected to one end of an equivalent resistor R_eq2And the other end of the same diode D_eq2Anode and equivalent resistance R_eq3The other end of the bridge arm is connected with the other end of the bridge arm to be used as a negative electrode of the bridge arm equivalent circuit.

Further, for any bridge arm of the MMC, the parameters of each equivalent element in the equivalent circuit of the bridge arm are calculated and determined through the following formula;

R_{temp1_j}(t)＝R_{Cbat0_j}(t)·R_{bat0_j}(t)/[R_{Cbat0_j}(t)+R_{bat0_j}(t)]+R_{bat1_j}(t)+R_{L1_j}(t)

R_{temp2_j}(t)＝R_{4_j}(t)·R_{temp1_j}(t)/[R_{4_j}(t)+R_{temp1_j}(t)]+R_{3_j}(t)

R_{temp3_j}(t)＝R_{C0_j}(t)·R_{temp2_j}(t)/[R_{C0_j}(t)+R_{temp2_j}(t)]

U_{temp1_j}(t)＝-U_{ceq1_j}(t)·R_{bat0_j}(t)/[R_{Cbat0_j}(t)+R_{bat0_j}(t)]+U_{bat0_j}(t)+U_{leq1_j}(t)

U_{temp2_j}(t)＝U_{temp1_j}(t)·R_{4_j}(t)/[R_{4_j}(t)+R_{temp1_j}(t)]

U_{temp3_j}(t)＝[U_{temp2_j}(t)·R_{C0_j}(t)+U_{ceq0_j}(t)·R_{temp2_j}(t)]/[R_{C0_j}(t)+R_{temp2_j}(t)]

U_{ceq0_j}(t)＝U_{C0_j}(t)+R_{C0_j}(t)·i_{C0_j}(t)

U_{ceq1_j}(t)＝U_{Cbat0_j}(t)+R_{Cbat0_j}(t)·i_{Cbat0_j}(t)

U_{leq1_j}(t)＝U_{L1_j}(t)+R_{L1_j}(t)·i_{L1_j}(t)

R_{bat0_j}(t)＝r_bat0R_{bat1_j}(t)＝r_bat1U_{bat0_j}(t)＝u_bat0

wherein: u shape_eq1(t) represents the equivalent voltage source U at time t_eq1Voltage value of U_eq2(t)Represents the equivalent voltage source U at the moment t_eq2Voltage value of R_eq1(t) represents the equivalent resistance R at time t_eq1Resistance value of R_eq2(t) represents the equivalent resistance R at time t_eq2Resistance value of R_eq3(t) represents the equivalent resistance R at time t_eq3A represents the set formed by all the sub-modules in the locking state in the current bridge arm, B represents the set formed by all the sub-modules in the normal operation state in the current bridge arm, j represents any sub-module in the bridge arm, R_{C0_j}(t)、R_{Cbat0_j}(t) and R_{L1_j}(t) respectively representing capacitors C in the bridge arm submodule j at the moment of t₀Lithium battery capacitor C_bat0And an inductance L₁Equivalent resistance value of R_{1_j}(t)～R_{4_j}(T) respectively representing IGBT tubes T in bridge arm submodule j at time T₁～T₄Equivalent resistance value of U_{C0_j}(t)、U_{Cbat0_j}(t) and U_{L1_j}(t) respectively representing capacitors C in the bridge arm submodule j at the moment of t₀Lithium battery capacitor C_bat0And an inductance L₁Voltage of i_{C0_j}(t)、i_{Cbat0_j}(t) and i_{L1_j}(t) respectively representing capacitors C in the bridge arm submodule j at the moment of t₀Lithium battery capacitor C_bat0And an inductance L₁C is a current of₀For the capacitance C in the submodule₀Capacity of c_bat0For the capacitor C of the lithium battery in the submodule_bat0Capacity value of l₁For the inductance L in the submodule₁Sensitivity value of r_bat0And r_bat1Respectively, the resistance R of the lithium battery in the submodule_bat0And R_bat1Resistance value of u_bat0For ideal voltage source U of lithium battery in submodule_bat0The remaining variables are intermediate variables.

Further, for any bridge arm of the MMC, calculating the electric quantity of each submodule at the t + delta t moment in the bridge arm by the following formula;

i_{C0_j}(t+Δt)＝[i_{csm_j}(t+Δt)·R_{temp2_j}(t+Δt)+U_{temp2_j}(t+Δt)-U_{ceq0_j}(t)]/[R_{temp2_j}(t+Δt)+R_{C0_j}(t+Δt)]

U_{C0_j}(t+Δt)＝U_{ceq0_j}(t)+R_{C0_j}(t+Δt)·i_{C0_j}(t+Δt)

U_{L1_j}(t+Δt)＝R_{L1_j}(t+Δt)·i_{L1_j}(t+Δt)-U_{leq1_j}(t)

i_{Cbat0_j}(t+Δt)＝[i_{L1_j}(t+Δt)·R_{bat0_j}(t+Δt)-U_{ceq1_j}(t)]/[R_{bat0_j}(t+Δt)+R_{Cbat0_j}(t+Δt)]

U_{Cbat0_j}(t+Δt)＝U_{ceq1_j}(t)+R_{Cbat0_j}(t+Δt)·i_{Cbat0_j}(t+Δt)

R_{temp2_j}(t+Δt)＝R_{4_j}(t+Δt)·R_{temp1_j}(t)/[R_{4_j}(t+Δt)+R_{temp1_j}(t)]+R_{3_j}(t+Δt)

U_{temp2_j}(t+Δt)＝U_{temp1_j}(t)·R_{4_j}(t+Δt)/[R_{4_j}(t+Δt)+R_{temp1_j}(t)]

R_{temp3_j}(t+Δt)＝R_{C0_j}(t+Δt)·R_{temp2_j}(t+Δt)/[R_{C0_j}(t+Δt)+R_{temp2_j}(t+Δt)]

U_{temp3_j}(t+Δt)＝[U_{temp2_j}(t+Δt)·R_{C0_j}(t+Δt)+U_{ceq0_j}(t)·R_{temp2_j}(t+Δt)]/[R_{C0_j}(t+Δt)+R_{temp2_j}(t+Δt)]

R_{bat0_j}(t+Δt)＝r_bat0R_{bat1_j}(t+Δt)＝r_bat1

wherein: u shape_{C0_j}(t+Δt)、U_{Cbat0_j}(t + Δ t) and U_{L1_j}(t + delta t) respectively represents the capacitor C in the bridge arm submodule j at the moment of t + delta t₀Lithium battery capacitor C_bat0And an inductance L₁Voltage of i_{C0_j}(t+Δt)、i_{Cbat0_j}(t + Δ t) and i_{L1_j}(t + delta t) respectively represents the capacitor C in the bridge arm submodule j at the moment of t + delta t₀Lithium battery capacitor C_bat0And an inductance L₁Current of R_{C0_j}(t+Δt)、R_{Cbat0_j}(t + Δ t) and R_{L1_j}(t + delta t) respectively represents the capacitor C in the bridge arm submodule j at the moment of t + delta t₀Lithium battery capacitor C_bat0And an inductance L₁Equivalent resistance value of R_{1_j}(t+Δt)～R_{4_j}(T + delta T) respectively represents IGBT tube T in bridge arm submodule j at the moment of T + delta T₁～T₄The other variables are intermediate variables.

Further, the latching current i_csm(t + delta t) is equivalent resistance R in the bridge arm equivalent circuit at the moment of t + delta t_eq2The current of (2).

Based on the technical scheme, the invention has the following beneficial technical effects:

1. for the lithium battery energy storage type MMC, the invention fills the blank of equivalent simulation modeling based on a discretization adjoint model method, and can provide a certain reference for future engineering design.

2. The invention has strong universality, and theoretically, the equivalent simulation method is not only suitable for the condition that all the submodules in the bridge arm normally operate or all the submodules are locked, but also suitable for the condition that some submodules in the bridge arm are locked.

Drawings

FIG. 1 is a schematic structural diagram of an MMC.

Fig. 2(a) is a schematic structural diagram of an energy storage type sub-module.

Fig. 2(b) is an equivalent circuit schematic diagram of the energy storage lithium battery in the sub-module.

FIG. 3 is a schematic diagram of an MMC bridge arm equivalent circuit.

Fig. 4 is a schematic diagram of a two-terminal unipolar dc power transmission system.

Fig. 5(a) is a voltage waveform diagram of the upper arm of phase a in the converter station 1 obtained by the equivalent simulation of the present invention.

FIG. 5(b) is a diagram showing the capacitor C of the sub-module of the upper bridge arm in phase A in the converter station 1 obtained by the equivalent simulation of the present invention₀Voltage waveform diagram of (2).

FIG. 5(c) is a diagram showing the flowing inductance L in the upper bridge arm submodule of phase A in the converter station 1 obtained by the equivalent simulation of the present invention₁Current waveform diagram of (2).

FIG. 5(d) is a diagram showing the equivalent capacitance C of the lithium battery in the sub-module of the upper bridge arm of phase A in the converter station 1 obtained by the equivalent simulation of the present invention_bat0Voltage waveform diagram of (2).

Detailed Description

In order to more specifically describe the present invention, the following detailed description is provided for the technical solution of the present invention with reference to the accompanying drawings and the specific embodiments.

As shown in fig. 4, the direct-current transmission system of the present embodiment is a two-end monopole system, the converter station 1 and the converter station 2 both adopt MMC, the MMC is a three-phase six-leg structure, and each leg is composed of a leg reactance and N energy storage type sub-modules connected in series, as shown in fig. 1; the energy storage sub-module is composed of 4 IGBT tubes T₁～T₄4 anti-parallel diodes D₁～D ₄1 sub-module capacitor C ₀1 reactance L₁And a circuit configuration of an energy storage lithium battery, as shown in fig. 2 (a); the equivalent circuit of the energy storage lithium battery is a first-order RC circuit and is composed of 1 ideal voltage source U_bat0Two resistors R_bat0～R_bat1And a capacitor C_bat0Composition, as shown in FIG. 2 (b).

The rated direct current voltage of the system is +400kV, the rated direct current power is 400WM, and the rest system parameters are shown in Table 1:

TABLE 1

It is pointed out that in the simulation, the converter station 1 adopts constant direct-current voltage and constant reactive power control, and the instruction values are 400kV and 0MVar respectively; the converter station 2 adopts constant active power control and constant reactive power, and the instruction values are-400 MW and 0MVar respectively; in the simulation, the currents flowing out of the lithium batteries in the submodules of the converter station 1 and the converter station 2 are controlled to be zero; in addition, all the sub-modules are considered to work normally in the simulation, no sub-module is in a locking state, and the simulation step size is 20 us.

Under normal operating condition, the energy storage type sub-module can output positive level and zero level: when T is₁Is on and T₂When the module is turned off, the submodule outputs a positive level; when T is₁Off and T₂When conducting, the submodule outputs zero level. In practice, T₃And T₄Only one of them is in the conducting state; using the reference world Group B4.58.control methods for direct voltage and power flow in a sampled HVDC grid [ R]The control method in Paris: CIGRE,2017:37-38, can be carried out by changing T₃And T₄On-off state of the current through L₁And (2) current, so that the control of the release/absorption power of the lithium battery is realized, and then equivalent simulation is carried out in the MMC converter station by using a voltage balance control strategy according to the following method:

(1) obtaining MMC operation parameters including bridge arm currents and T in submodules₁～T₄The switch state of (1).

Obtaining the operating parameters of the bridge arm comprises the bridge arm current i_armAnd a latching current i_cmsSince no submodule is in a locked state, only the bridge arm current i needs to be acquired_armThen the method is finished; obtaining T₁～T₄The switch state of (1).

(2) And respectively constructing equivalent circuits of all bridge arms of the MMC according to the MMC operation parameters, and determining the parameters of all equivalent elements in the bridge arm equivalent circuits.

The equivalent circuit of the bridge arm is shown in FIG. 3 and consists of 3 equivalent resistors R_eq1～R_eq3Two equivalent voltage sources U_eq1And U_eq2And two equivalent diodes D_eq1And D_eq2Forming; wherein, the equivalent voltage source U_eq1The positive pole of the equivalent circuit is the positive pole of the equivalent circuit of the bridge arm, and the equivalent voltage source U_eq1And the equivalent resistance R_eq1Is connected to one end of an equivalent resistor R_eq1And the other end of the same diode D_eq1Anode of (2), equivalent diode D_eq2And the equivalent resistance R_eq3Is connected to an equivalent diode D_eq1Cathode and equivalent voltage source U of_eq2Is connected with the anode of the equivalent voltage source U_eq2And the equivalent resistance R_eq2Is connected to one end of an equivalent resistor R_eq2And the other end of the same diode D_eq2Anode and equivalent resistance R_eq3The other end of the bridge arm is connected to form the cathode of the equivalent circuit of the bridge arm.

(3) And establishing a simulation model of the MMC according to the bridge arm equivalent circuit, and carrying out simulation calculation on the system based on the t-moment electric quantity of the sub-module in the bridge arm to obtain the t + delta t-moment electric quantity of the external circuit.

3 equivalent resistors R in equivalent bridge arm at time t_eq1(t)～R_eq3(t) and two equivalent voltage sources U_eq1(t) and U_eq2(t) can be calculated by the following formula:

R_{bat0_j}(t)＝R_bat0＝0.164Ω

R_{bat1_j}(t)＝R_bat1＝0.5Ω

U_{bat0_j}(t)＝U_bat0＝1.0kV

U_{ceq1_j}(t)＝U_{Cbat0_j}(t)+R_{Cbat0_j}(t)·i_{Cbat0_j}(t)

U_{leq1_j}(t)＝U_{L1_j}(t)+R_{L1_j}(t)·i_{L1_j}(t)

R_{temp1_j}(t)＝R_{Cbat0_j}(t)·R_{bat0_j}(t)/[R_{Cbat0_j}(t)+R_{bat0_j}(t)]+R_{bat1_j}(t)+R_{L1_j}(t)

U_{temp1_j}(t)＝-U_{ceq1_j}(t)·R_{bat0_j}(t)/[R_{Cbat0_j}(t)+R_{bat0_j}(t)]+U_{bat0_j}(t)+U_{leq1_j}(t)

R_{temp2_j}(t)＝R_{4_j}(t)·R_{temp1_j}(t)/[R_{4_j}(t)+R_{temp1_j}(t)]+R_{3_j}(t)

U_{temp2_j}(t)＝U_{temp1_j}(t)·R_{4_j}(t)/[R_{4_j}(t)+R_{temp1_j}(t)]

U_{ceq0_j}(t)＝U_{C0_j}(t)+R_{C0_j}(t)·i_{C0_j}(t)

R_{temp3_j}(t)＝R_{C0_j}(t)·R_{temp2_j}(t)/[R_{C0_j}(t)+R_{temp2_j}(t)]

U_{temp3_j}(t)＝[U_{temp2_j}(t)·R_{C0_j}(t)+U_{ceq0_j}(t)·R_{temp2_j}(t)]/[R_{C0_j}(t)+R_{temp2_j}(t)]

U_eq2(t)＝0kV

R_eq2(t)＝0Ω

wherein: (t) represents a variable value at the moment t, delta t represents a simulation step length, and subscript _ j represents that the variable belongs to the jth sub-module in the bridge arm; r_{C0_j}(t)，R_{Cbat0_j}(t) and R_{L1_j}(t) is respectively expressed as a sub-module capacitor C in the jth sub-module in the bridge arm at the moment t₀Lithium battery equivalent capacitor C_bat0And a reactance L₁The equivalent resistance value of (1); r_{1_j}(t)～R_{4_j}(T) denotes time T₁～T₄The equivalent resistance value of (1); u shape_{C0_j}(t)、U_{Cbat0_j}(t) and U_{L1_j}(t) respectively representing sub-module capacitors C in jth sub-module in bridge arm at t moment₀Voltage, equivalent capacitance C of lithium battery_bat0Voltage and L₁Voltage of (d); i.e. i_{C0_j}(t)、i_{Cbat0_j}(t) and i_{L1_j}(t) respectively representing sub-module capacitors C in jth sub-module in bridge arm at t moment₀Current, lithium cell equivalent capacitance C_bat0Current and L₁The remaining variables are intermediate variables.

And then solving the whole external circuit to obtain the electric quantity of the external circuit at the time of t + delta t.

(4) Bridge arm current i at the moment of t + delta t calculated in the previous step_arm(t + Δ t) and a blocking current i_csmAnd (t + delta t), calculating the voltage and the current of the capacitor and the inductor in each submodule of the bridge arm at the moment of t + delta t based on the equivalent circuit of the bridge arm.

Because no submodule is in a locking state, the voltage and the current of the capacitor and the inductor in each submodule of the bridge arm at the moment of t + delta t can be calculated by the following formula:

R_{bat0_j}(t+Δt)＝R_bat0＝0.164Ω

R_{bat1_j}(t+Δt)＝R_bat1＝1.0kV

i_{csm_j}(t+Δt)＝[i_arm(t+Δt)·R_{2_j}(t+Δt)-U_{temp3_j}(t)]/R_{2_j}(t+Δt)+R_{1_j}(t+Δt)+R_{temp3_j}(t)

R_{temp2_j}(t+Δt)＝R_{4_j}(t+Δt)·R_{temp1_j}(t)/[R_{4_j}(t+Δt)+R_{temp1_j}(t)]+R_{3_j}(t+Δt)

U_{temp2_j}(t+Δt)＝U_{temp1_j}(t)·R_{4_j}(t+Δt)/[R_{4_j}(t+Δt)+R_{temp1_j}(t)]

R_{temp3_j}(t+Δt)＝R_{C0_j}(t+Δt)·R_{temp2_j}(t+Δt)/[R_{C0_j}(t+Δt)+R_{temp2_j}(t+Δt)]

U_{temp3_j}(t+Δt)＝[U_{temp2_j}(t+Δt)·R_{C0_j}(t+Δt)+U_{ceq0_j}(t)·R_{temp2_j}(t+Δt)]/[R_{C0_j}(t+Δt)+R_{temp2_j}(t+Δt)]

i_{C0_j}(t+Δt)＝[i_{csm_j}(t+Δt)·R_{temp2_j}(t+Δt)+U_{temp2_j}(t+Δt)-U_{ceq0_j}(t)]/[R_{temp2_j}(t+Δt)+R_{C0_j}(t+Δt)]

U_{C0_j}(t+Δt)＝U_{ceq0_j}(t)+R_{C0_j}(t+Δt)·i_{C0_j}(t+Δt)

U_{L1_j}(t+Δt)＝R_{L1_j}(t+Δt)·i_{L1_j}(t+Δt)-U_{leq1_j}(t)

i_{Cbat0_j}(t+Δt)＝[i_{L1_j}(t+Δt)·R_{bat0_j}(t+Δt)-U_{ceq1_j}(t)]/[R_{bat0_j}(t+Δt)+R_{Cbat0_j}(t+Δt)]

U_{Cbat0_j}(t+Δt)＝U_{ceq1_j}(t)+R_{Cbat0_j}(t+Δt)·i_{Cbat0_j}(t+Δt)

wherein: (t + delta t) represents the value of the variable at the moment of t + delta t, delta t represents the simulation step length, and subscript _ j represents that the variable belongs to the jth submodule in the bridge arm; r_{C0_j}(t+Δt)，R_{Cbat0_j}(t + Δ t) and R_{L1_j}(t + delta t) is respectively expressed as a sub-module capacitor C in the jth sub-module in the bridge arm at the moment of t + delta t₀Lithium battery equivalent capacitor C_bat0And a reactance L₁The equivalent resistance value of (1); r_{1_j}(t+Δt)～R_{4_j}(T + Δ T) represents the time T at T + Δ T₁～T₄The equivalent resistance value of (1); u shape_{C0_j}(t+Δt)、U_{Cbat0_j}(t + Δ t) and U_{L1_j}(t + delta t) respectively represents the sub-module capacitor C in the jth sub-module in the bridge arm at the moment of t + delta t₀Voltage, equivalent capacitance C of lithium battery_bat0Voltage and L₁Voltage of (d); i.e. i_{C0_j}(t+Δt)、i_{Cbat0_j}(t + Δ t) and i_{L1_j}(t + delta t) respectively represents the sub-module capacitor C in the jth sub-module in the bridge arm at the moment of t + delta t₀Current, lithium cell equivalent capacitance C_bat0Current and L₁The current of (a); the remaining variables are intermediate variables.

FIGS. 5(a) to 5(d) respectively show the upper bridge arm voltage of phase A and the sub-module capacitor C in the converter station 1 obtained by the equivalent simulation method of the present invention₀Voltage, flowing through reactance L in submodule₁Current and lithium battery equivalent capacitor C in submodule_bat0The simulation waveform of the voltage, and the analysis result can find the effectiveness of the method.

The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.