CN111555335B - Coordinated control method of self-energy storage multi-terminal back-to-back flexible-straightening system based on master-slave control - Google Patents
Coordinated control method of self-energy storage multi-terminal back-to-back flexible-straightening system based on master-slave control Download PDFInfo
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Abstract
本发明公开了一种基于主从控制的自储能多端背靠背柔直系统协调控制方法。包括如下步骤：步骤一：建立协调控制策略整体框架；步骤二：判断直流母线电压波动量是否超过直流母线电压指令值的1%，建立若干种系统运行工况；步骤三：针对步骤二得到的各种系统运行工况，确定主换流器、储能DC/DC变换器、从换流器的详细的协调控制方式。解决了主从控制及其改进电压裕度控制策略对直流系统功率的动态调节能力不足，系统功率波动时易引起较大的直流电压波动问题。对储能单元二次调节过程的时间参数进行了整定，防止储能单元二次调节过程过快而引起直流电压二次波动。仿真验证了所提控制策略的可行性和有效性。
The invention discloses a self-energy storage multi-terminal back-to-back flexible-straightening system coordinated control method based on master-slave control. It includes the following steps: Step 1: establish the overall framework of the coordinated control strategy; Step 2: determine whether the DC bus voltage fluctuation exceeds 1% of the DC bus voltage command value, and establish several system operating conditions; Various system operating conditions, determine the detailed coordinated control mode of the main converter, energy storage DC/DC converter, and slave converters. It solves the problem that the master-slave control and its improved voltage margin control strategy have insufficient dynamic adjustment ability to the DC system power, and the system power fluctuation is likely to cause large DC voltage fluctuations. The time parameters of the secondary adjustment process of the energy storage unit are set to prevent the secondary adjustment of the energy storage unit from causing the secondary fluctuation of the DC voltage. Simulations verify the feasibility and effectiveness of the proposed control strategy.
Description
Technical Field
The invention relates to the field of multi-terminal flexible direct current power transmission and distribution and the field of power electronics, in particular to a self-energy-storage multi-terminal back-to-back flexible direct current system coordination control strategy based on master-slave control.
Background
The multi-end back-to-back flexible control technology is a newly developed power grid flexible control technology, can realize the safe loop closing operation of a feeder line, accurately regulates and controls the power grid tide distribution, and improves the power supply reliability and the operation economy. The energy storage technology can convert electric energy into other capacity forms which are easy to store for storage, and has electric energy transfer capacity in a time dimension. The multi-end back-to-back flexible and straight 'AC-DC-AC' working mode also makes it possible to blend with the depth of the energy storage unit.
The self-energy-storage multi-end back-to-back flexible-straight system integrates the two energy regulation and control technologies, a multi-end flexible interconnected power distribution network with 'source, network, load, storage and control' can be constructed, the optimal control capability of the multi-end flexible interconnected power distribution network is enhanced more effectively, and the self-energy-storage multi-end back-to-back flexible-straight system has important significance for improving the distributed energy consumption level and the power supply reliability. Currently, there is very little research on the control strategy of a self-energy-storage multi-end back-to-back flexible direct system.
The master-slave control is a classical control strategy of a multi-terminal flexible direct current system, and when the system operates, one converter is selected as a master converter to maintain the power balance of the system and control the direct current voltage to be stable. However, the control strategy puts high demands on the performance of the main converter, the dynamic adjustment capability of the main converter on the transmission power of the system is insufficient, and the power adjustment margin is influenced by the transmission power, so that when the power of the direct current system fluctuates, the direct current bus voltage is easy to fluctuate greatly, and the dynamic stability of the direct current voltage is poor.
Disclosure of Invention
The invention aims to provide a direct-current voltage coordination control strategy method of a self-energy-storage multi-end back-to-back flexible direct-current system based on master-slave control, which is used for solving the defects of the traditional master-slave control strategy in the dynamic regulation process of the direct-current bus voltage of the system.
In order to achieve the above object, the scheme of the invention comprises the following contents:
a self-energy-storage multi-end back-to-back flexible-direct system coordination control method based on master-slave control is characterized by comprising the following steps:
the method comprises the following steps: establishing a coordination control strategy overall framework;
step two: judging whether the fluctuation quantity of the direct current bus voltage exceeds 1% of a direct current bus voltage instruction value or not, and establishing a plurality of system operation working conditions;
step three: determining detailed coordination control modes of the main converter, the energy storage DC/DC converter and the auxiliary converter according to various system operation conditions obtained in the step two;
step four: and after the system is regulated and is in the state that the fluctuation quantity of the direct current bus voltage is less than or equal to 1% of the direct current bus voltage command value again from other working conditions, the energy storage DC/DC converter is subjected to secondary regulation.
Establishing a coordination control strategy overall framework in the first step, wherein the specific process is as follows: when the self-energy-storage multi-end back-to-back flexible direct-current system is in a steady-state operation process, the main converter adopts a constant direct-current voltage control mode to maintain system power balance and direct-current voltage stability, and the energy-storage DC/DC and the auxiliary converter are in a constant power control mode; the steady-state operation process is that the fluctuation quantity of the direct-current voltage is less than or equal to 1% of the direct-current bus voltage instruction value; when the system is in a dynamic adjusting process, the energy storage DC/DC converter is converted into a constant direct current voltage control mode to maintain power balance and inhibit voltage fluctuation of a direct current bus, the main converter is converted into a constant power mode, and the auxiliary converter is in a constant power mode.
Establishing a plurality of system operation conditions in the second step: the specific working conditions comprise:
under the working condition I, the fluctuation quantity of the direct current bus voltage is less than or equal to 1% of the direct current bus voltage instruction value;
under the second working condition, the fluctuation amount of the direct current bus voltage exceeds 1% of the direct current bus voltage instruction value, but the system power fluctuation does not exceed the power regulation margin of the main converter;
under the third working condition, the fluctuation amount of the direct current bus voltage exceeds 1% of the direct current bus voltage instruction value, and the system power fluctuation exceeds the power regulation margin of the main converter;
and under the fourth working condition, the main converter is out of operation due to faults.
In the third step, the coordination control mode of the main converter, the energy storage DC/DC converter and the slave converter is determined according to the operation conditions of various systems obtained in the second step;
under each working condition, a constant direct current voltage control mode of the main converter adopts a constant direct current voltage control mode, a constant power control mode adopts a constant power control mode, an energy storage DC/DC constant direct current voltage control mode adopts a virtual direct current motor control mode, and the constant power control mode adopts a constant power control mode; the control mode adopted by the slave converter in different control modes is the same as that of the master converter.
In the fourth step, the energy storage DC/DC converter performs the second timeThe time required for adjustment is more than or equal to Tmin，TminComprises the following steps:
wherein, PessIn order to dynamically adjust the transmission power of the system which is still maintained by the stored energy DC/DC when the system enters the working condition again from other working conditions, delta t is the time required by the main converter to respond to the power change of the system, C is the direct current bus capacitor of the system, and delta U isdc.maxThe secondary regulation process for energy storage allows the maximum value of the fluctuation quantity of the direct current bus voltage to be caused.
The invention provides a coordination control strategy based on master-slave control on the basis of an established self-energy-storage multi-end back-to-back flexible-direct model, and the dynamic regulation capability of system power and the dynamic stability performance of direct-current bus voltage are improved by utilizing a main current converter and an energy storage unit to cope with the steady-state operation and dynamic regulation process of a system in a combined mode. And the system coordination control process is designed in detail according to a plurality of typical system operation conditions, so that the system can effectively deal with different operation conditions and can safely and stably operate. The problem that dynamic regulation capacity of master-slave control and an improved voltage margin control strategy for the power of a direct current system is insufficient, and large direct current voltage fluctuation is easily caused when the power of the system fluctuates is solved. The time parameter of the energy storage unit in the secondary adjustment process is adjusted, and secondary fluctuation of the direct-current voltage caused by the fact that the secondary adjustment process of the energy storage unit is too fast is prevented. The feasibility and the effectiveness of the control strategy are verified through simulation.
Drawings
Fig. 1 is a self-storing multi-terminal back-to-back flexible-straight system topology.
Fig. 2(a) is a schematic diagram of the system control in the steady state.
Fig. 2(b) is a schematic diagram of the system control in the transient state.
Fig. 3 is a schematic diagram of switching control modes of each port of the system.
Fig. 4(a) is a simulation result of power of each port under the operating condition two-coordination control strategy.
FIG. 4(b) is a simulation result of power of each port under the conventional margin control under the second operating condition.
FIG. 4(c) shows the simulation result of the DC bus voltage under the second operating condition.
Fig. 5(a) is a simulation result of power of each port under the three-coordination control strategy under the operating condition.
Fig. 5(b) is a simulation result of power of each port under three conventional margin controls under the operating condition.
Fig. 5(c) is a simulation result of three dc bus voltages under operating conditions.
Fig. 6(a) is a simulation result of power of each port under the four-coordination control strategy under the operating condition.
Fig. 6(b) is a simulation result of four dc bus voltages under operating conditions.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clear and more obvious, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.
The self-energy-storage multi-end back-to-back flexible straight system structure topology adopts a back-to-back parallel structure, and the structure is easy to expand and high in reliability. The self-energy-storage multi-end back-to-back flexible and straight control system can be divided into system-level control, converter-level control and converter valve-level control. The invention discloses a self-energy-storage multi-end back-to-back flexible direct current system coordination control strategy, belongs to system-level control, and is used for coordinating the control mode of each converter of a system and maintaining the voltage stability of a direct current bus.
The VSC converter level control modes are as follows: constant power control and constant direct current voltage control. The control modes of the energy storage DC/DC converter are as follows: virtual DC motor control and constant power control.
The tasks of maintaining the steady-state operation and dynamic regulation of the system of the self-energy-storage multi-end back-to-back flexible-straight system are respectively undertaken by the main current converter and the energy-storage DC/DC converter, and when the system operates, the system sends out control signals to control the switching control mode of each port.
Fig. 2(a) and 2(b) are schematic diagrams showing system control, and fig. 2(a) is a schematic diagram showing the system control in a steady state; fig. 2(b) is a schematic diagram of the system control in the transient state. When the self-energy-storage multi-end back-to-back flexible direct-current system operates in a steady state, the main converter is controlled by constant direct-current voltage, and the rest VSC and the energy-storage DC/DC are controlled by constant power. The energy storage unit can receive a power grid dispatching instruction to realize the regulation and control of the system on the energy in time and space. At the moment, the main converter bears the steady-state transmission power of the system and controls the voltage of the direct-current bus, but the dynamic control capability of the voltage of the direct-current bus is insufficient, and the power regulation margin is influenced by the steady-state transmission power.
When the system is disturbed or failed and the voltage fluctuation of the direct-current bus is large, the main converter enters a constant-power operation mode, the energy storage unit undertakes the dynamic adjustment task of the system, the rapid power adjustment characteristic of the energy storage unit is fully exerted, and the voltage fluctuation of the direct-current bus is restrained. The energy storage unit adjusting process can be divided into the following two processes:
(1) the primary adjustment process of the energy storage unit: when the voltage fluctuation of the direct current bus is large, the system sends control mode switching signals to the main current converter and the energy storage unit. The energy storage unit is switched to a direct-current voltage control mode to replace a main converter, the power quick dynamic response capability of the energy storage unit is exerted, the system power is dynamically adjusted, and the voltage mutation of a direct-current bus is restrained.
(2) And (3) secondary adjustment process of the energy storage unit: when the voltage of the direct current bus is stable, the system sends control signals to the main current converter and the energy storage unit again, and the main current converter and the energy storage unit are switched back to the constant power control mode. At this time, the energy storage DC/DC may bear a part of the system transmission power. Therefore, the power dynamic adjustment margin of the energy storage DC/DC can not be influenced by the steady-state transmission power, and the use cost and the service life of the energy storage are reduced. The energy storage unit needs to be adjusted for the second time, in the process, the energy storage DC/DC slowly reduces the output power to zero, and the power is transferred to the main converter to be borne, so that the energy storage unit is restored to the state before the primary adjustment process.
The control strategy can fully exert the power transmission capability of the main converter and the dynamic power regulation capability of the energy storage unit, ensure the high-precision transmission of the system power in a steady state, simultaneously enhance the voltage control capability of the dynamic direct current bus and ensure that the dynamic power regulation margin is not influenced by the steady-state transmission power.
The control mode switching flow of each port of the system is shown in fig. 3.
In order to ensure that the self-energy-storage multi-end back-to-back flexible-straight system can keep safe and stable operation under different working conditions, the coordination working mechanism of the energy storage unit and other ports under four different working conditions needs to be researched. The system operation conditions are divided into four according to the condition that the system is disturbed or has faults, and a coordination mechanism between the energy storage unit and each port of the system is established according to each operation condition. And selecting the VSC1 as a master converter and the VSC2 as a slave converter.
The first operation condition is as follows: under the working condition, the voltage of the voltage bus fluctuates
Within the range of (
Is the system DC bus voltage UdcThe command value) of (1%), the fluctuation amount of the direct current bus voltage is less than or equal to 1% of the direct current bus voltage command value; VSC1 adopts and decides direct current voltage control balanced system transmission power and stable direct current busbar voltage, and VSC2 and energy storage unit all adopt and decide power control. When the system operates under the working condition, the problems of energy storage use cost and service life are considered, the energy storage unit does not participate in the work of controlling the direct-current bus voltage of the system, and only receives power grid dispatching and SOC recovery work.
And a second operation condition: under the working condition, the voltage fluctuation of the direct current bus exceeds that of the system after the system is disturbed
But the system power fluctuations do not exceed the power regulation margin of the main converter. That is: the voltage fluctuation of the direct current bus exceeds 1% of the direct current bus voltage command value, but the system power fluctuation is less than or equal to the power regulation margin of the main converter. In this condition, in order to suppress the voltage fluctuation of the dc bus, the energy storage unit is required to suppress the voltage fluctuation of the dc bus by using its fast charging and discharging characteristics. At the moment of disturbance, the main converter is switched to constant power control, and meanwhile, the energy storage unit is switched to constant direct current voltage control to enter a primary regulation process to control the direct current bus voltage. During transient regulationThe energy unit can effectively restrain the voltage fluctuation of the direct current bus by utilizing the rapid dynamic power response capability. After the dc voltage is stabilized, the VSC1 switches back to constant dc voltage control again, and at the same time, the energy storage unit switches back to constant power control. After the energy storage unit adjusts the system power for the first time and the direct-current voltage is stabilized, the power is switched back to the constant power control and the secondary adjustment is carried out.
And the operation working condition is three: under the working condition, the fluctuation of the DC bus voltage exceeds
And the system power fluctuation exceeds the power regulation margin of the VSC1 of the main converter; that is to say: the voltage fluctuation of the direct current bus exceeds 1% of the voltage command value of the direct current bus, and the power fluctuation of the system exceeds the power regulation margin of the main converter; and during transient adjustment, the coordination control process and the operation working condition of each port of the system are the same. After transient regulation, when the energy storage unit performs secondary regulation, the main converter enters a current limiting mode because the main converter reaches the upper limit of power transmission and operates at the maximum power. At the moment, the control mode of the energy storage unit is switched back to the constant direct current voltage control again, the voltage of the direct current bus is maintained to be stable, and the balance unbalanced power is borne. After the disturbance is eliminated, the energy storage unit can perform secondary regulation again, and the system is restored to the state of the first operating condition.
And the operation working condition is four: under this condition, the main converter quits operation due to faults. When a fault occurs, the energy storage unit is switched to a constant direct current voltage control mode to maintain the power balance of the system and control the direct current bus voltage, but the power regulation margin of the energy storage unit is possibly exceeded under the condition. If so, the energy storage unit enters a current limiting mode and operates with maximum power discharge, and at the moment, UdcThe voltage of the direct current bus can continuously drop to
At this time, the control method is switched from the VSC2 control method to the constant dc voltage control. After the fault is eliminated, the power command of each port is adjusted by the power grid dispatching to enable the system to be recovered to the first operation condition.
The mutual switching of the control modes of the main converter VSC1 and the energy storage unit, which are analyzed above, depends on the communication of the system. The system adopts voltage margin control from the VSC2, so that when communication faults occur, the system is equivalently changed into the traditional voltage margin control, and the operation reliability of the system can be effectively improved.
In the dynamic adjustment process of the energy storage unit, inertia and damping can be provided for a direct current system through a direct current voltage outer ring and a virtual direct current motor link, and the voltage stability of a direct current bus is effectively enhanced. However, after the dc bus voltage is stabilized due to the existence of the dc voltage outer ring, the energy storage unit can still continuously output or absorb power. This not only reduces the dynamic power adjustment margin of the energy storage unit, which is not favorable for the safe and stable operation of the system, but also increases the use cost of the energy storage unit. Therefore, after the voltage of the direct current bus is stabilized, the energy storage unit actively exits the current charge-discharge state through secondary regulation and restores to the operation state before the transient regulation process.
And the control mode during secondary regulation of the energy storage unit adopts DC/DC constant power control, and the power instruction of the energy storage unit changes to zero along with time.
However, when the energy storage unit performs secondary regulation, the power change should not be too fast, so as to avoid secondary fluctuation of the dc bus voltage, which is not beneficial to the safe and stable operation of the system. Therefore, the time of the secondary regulation process needs to be limited to prevent the secondary fluctuation of the dc bus voltage.
When the energy storage unit is adjusted for the second time, the generated power fluctuation can cause the voltage fluctuation of the direct current bus. The following formula:
wherein C is system DC bus capacitor, UdcThe system direct current bus voltage is obtained, and delta P is the power fluctuation amount of the energy storage unit.
When the energy storage unit performs secondary regulation to reduce the emitted or absorbed power, the energy shortage of the system will be borne by the dc bus capacitor in the Δ t time before the VSC1 does not respond to the system power change, which will cause the dc bus voltage to fluctuate as shown in formula (2):
ΔUdcand delta t is the time required by the VSC1 to respond to the system power change for the fluctuation quantity of the direct-current bus voltage caused by the energy storage secondary regulation process. Let delta Udc.maxThe maximum value of the fluctuation quantity of the direct current bus voltage allowed in the secondary energy storage regulation process can be obtained, and the system can bear the maximum power fluctuation quantity delta P in delta t timemaxAs shown in the following formula:
then, when the stored energy secondary regulation power is PessThen, the following formula can be obtained:
in the formula, PessThe transmission power (namely the total power required to be regulated in the process of secondary regulation of the stored energy) which is still maintained by the stored energy DC/DC when the system enters the working condition again from other working conditions through dynamic regulationminThe fluctuation amount of the direct current bus voltage caused by the secondary regulation process does not exceed delta Udc.maxThe shortest adjustment time in the case.
In the secondary adjustment process of the energy storage unit, the adjustment time is longer than TminThe system can be ensured to operate stably.
In order to prove the feasibility and the effectiveness of the system coordination control strategy, a four-terminal self-energy-storage back-to-back flexible-straight system model shown in FIG. 1 is built on the basis of Matlab/Simulink. The three-end VSC converter and the DC/DC converter are connected to a direct-current bus of the system in parallel back to back, the VSC alternating-current side is connected with an active power distribution network, and the DC/DC low-voltage side is connected with an energy storage unit. The system simulation parameters are shown in table 1.
TABLE 1 simulation System parameters
In the first operation condition, the system operates in a steady state, and both the power and the voltage have no obvious fluctuation, so that the first operation condition is not subjected to further simulation verification, and only three conditions, namely the second operation condition, the third operation condition and the fourth operation condition, of the system are subjected to simulation verification.
(1) Operating condition two
Under the initial operation state of the system, the output power of the VSC1, the output power of the energy storage DC/DC, the output power of the VSC2 and the output power of the VSC3 are respectively-3 MW, 0 MW, 1 MW and 2 MW. VSC3 active power increased from 2MW to 4MW at 0.2 seconds. Simulation results of the self-energy-storage multi-terminal back-to-back flexible direct system coordination control strategy based on the voltage margin control are shown in fig. 4(a) -4 (c).
Fig. 4(a) is a simulation result of power of each port under the operation condition two-coordination control strategy, and it can be seen that: DC bus voltage fluctuation exceeding 0.2 second
The energy storage DC/DC control mode is switched to constant direct-current voltage control, and the VSC1 control mode is switched to constant power control. After the virtual direct current motor is adopted to control a primary adjusting process, the energy storage unit can rapidly and dynamically adjust the system power, provide inertia and damping for the direct current bus and effectively inhibit direct current voltage fluctuation. Fig. 4(b) is a simulation result of power of each port under the operation condition two traditional margin control, and it can be seen that: and at 0.3 second, the control mode of the energy storage unit is switched to constant power control, secondary regulation is started, meanwhile, the control mode of the VSC1 is switched to constant direct-current voltage control, and the transmission power born by the energy storage DC/DC is handed over to the VSC 1. In the secondary adjustment process of the energy storage unit, the power change of each port of the system is stable, and secondary fluctuation of the direct-current bus voltage is not caused. At 0.6 seconds, the system power disturbance is eliminated and the system power returns to normal, but the rapid recovery of the VSC3 power also causes the dc bus voltage to fluctuate, so the system enters the same coordinated control process as at 0.3 seconds. FIG. 4(c) is a diagram of a modified coordinated control strategyThe power simulation results of each port under the control of the traditional margin under the second operating condition can be seen as follows: the system DC voltage fluctuates at
When the traditional master-slave control is adopted, the voltage fluctuation of the system exceeds
In the second working condition, the dynamic stability of the direct-current voltage of the system is better under the improved coordination control strategy.
(2) Operating condition three
Under the initial operation state of the system, the output power of the VSC1, the output power of the energy storage DC/DC, the output power of the VSC2 and the output power of the VSC3 are respectively-3.5, 0, 1.5 and 2 MW. The VSC2 increased from 1.5MW to 4.5MW at 0.2 seconds. The simulation results are shown in fig. 5(a) to 5 (c).
Fig. 5(a) is a simulation result of power of each port under the three-coordination control strategy under the operating condition, and it can be seen that: the control mode of the energy storage unit is switched to control the constant direct-current voltage in 0.2 second, the energy storage unit performs secondary regulation after the system is stable, but at a certain moment of secondary regulation, the output power of the VSC1 reaches the upper limit of power transmission, and at the moment, the VSC1 enters a constant power mode to run at full power. And the energy storage DC/DC is switched back to the control mode of the virtual direct current motor, the voltage of the direct current bus is stabilized, and the transmission power of the rest system is borne. Fig. 5(c) is a simulation result of three dc bus voltages under operating conditions, and it can be seen that: in the third operating condition of the system, the switching of each port is stable and smooth in the coordinated control process, and the fluctuation of the direct-current bus voltage does not exceed the fluctuation all the time
Under the traditional master-slave control, the VSC1 cannot stabilize the DC bus voltage due to the fact that the power regulation margin reaches the upper limit, and the DC voltage fluctuation exceeds
The slave VSC2 is switched to the master. Fig. 5(b) is a simulation result of power of each port under three conventional margin controls under the operating condition. In the third working condition, the dynamic stability of the direct-current voltage of the system is improved under the coordination control strategyAnd more preferably.
(3) Operating condition four
Under the working condition, the initial operation state of the system is the same as the second operation working condition. At 0.2 seconds, the VSC1 exited operation due to the fault. The simulation results are shown in fig. 6(a) and 6 (b). Fig. 6(a) is a simulation result of power of each port under the four-coordination control strategy under the operating condition, and fig. 6(b) is a simulation result of voltage of four direct-current buses under the operating condition.
As can be seen from fig. 6(a) and 6(b), after the VSC1 fails and stops operating, the system power is severely unbalanced, the energy storage unit cannot compensate the power shortage of the system after full power output, the dc voltage continues to drop, and the dc voltage drops to a level that is lower than the dc voltage
When the VSC2 control mode is switched to constant direct current voltage control, the system reaches balance under a new voltage level. The VSC2 employs margin control to ensure system reliability.
Claims (1)
1. A self-energy-storage multi-end back-to-back flexible-direct system coordination control method based on master-slave control is characterized by comprising the following steps:
the method comprises the following steps: establishing a coordination control strategy overall framework; when the self-energy-storage multi-end back-to-back flexible direct-current system is in a steady-state operation process, the main converter adopts a constant direct-current voltage control mode to maintain system power balance and direct-current voltage stability, and the energy-storage DC/DC converter and the auxiliary converter are in a constant power control mode; the steady-state operation process is that the fluctuation quantity of the direct-current bus voltage is less than or equal to 1% of the direct-current bus voltage instruction value; when the system is in a dynamic adjusting process, the energy storage DC/DC converter is converted into a constant direct current voltage control mode to maintain power balance and inhibit voltage fluctuation of a direct current bus, the main converter is converted into a constant power control mode, and the auxiliary converter is in a constant power control mode;
step two: judging whether the fluctuation quantity of the direct current bus voltage exceeds 1% of a direct current bus voltage instruction value or not, and establishing a plurality of system operation working conditions;
under the working condition I, the fluctuation quantity of the direct current bus voltage is less than or equal to 1% of the direct current bus voltage instruction value;
under the second working condition, the fluctuation amount of the direct current bus voltage exceeds 1% of the direct current bus voltage instruction value, but the system power fluctuation is less than or equal to the power regulation margin of the main converter;
under the third working condition, the fluctuation amount of the direct current bus voltage exceeds 1% of the direct current bus voltage instruction value, and the system power fluctuation exceeds the power regulation margin of the main converter;
under the working condition four, the main converter stops running due to faults;
step three: determining a coordination control mode of the main converter, the energy storage DC/DC converter and the slave converter according to various system operation conditions obtained in the step two;
under each working condition, a constant direct current voltage control mode of the main converter adopts a constant direct current voltage control mode, and a constant power control mode adopts a constant power control mode; the energy storage DC/DC converter adopts a virtual direct current motor control mode in a constant direct current voltage control mode, and adopts a constant power control mode in a constant power control mode;
the first operation condition is as follows: the main converter adopts constant direct current voltage to control the transmission power of the balance system and stabilize the direct current bus voltage, and the auxiliary converter and the energy storage DC/DC converter both adopt constant power control; when the system operates under the working condition, the energy storage DC/DC converter does not participate in the work of controlling the voltage of the direct current bus of the system, and only receives the dispatching of the power grid and the SOC recovery work;
and a second operation condition: in order to inhibit the voltage fluctuation of the direct current bus, the energy storage unit is required to inhibit the voltage fluctuation of the direct current bus by utilizing the rapid charging and discharging characteristics of the energy storage unit; at the moment of disturbance, the main converter is switched to constant power control, and meanwhile, the energy storage DC/DC converter is switched to constant direct current voltage control to enter a primary regulation process to control the voltage of a direct current bus; after the direct-current voltage is stabilized, the main converter is switched back to the constant direct-current voltage control, and meanwhile, the energy storage DC/DC converter is switched back to the constant power control; after the energy storage DC/DC converter adjusts the system power for the first time and the direct current voltage is stabilized, the system is switched back to the constant power control and adjusted for the second time;
and the operation working condition is three: during transient state adjustment, the coordination control process and the operation working condition of each port of the system are the same; after transient regulation, when the energy storage DC/DC converter performs secondary regulation, the main converter reaches the upper limit of power transmission and enters a current limiting mode to operate at the maximum power; at the moment, the control mode of the energy storage DC/DC converter is switched back to the constant direct current voltage control again, the voltage of the direct current bus is maintained to be stable, and the unbalanced power of the rest part is borne; after disturbance is eliminated, the energy storage DC/DC converter performs secondary regulation again, and the system is restored to the state of the first operating condition;
and the operation working condition is four: when a fault occurs, the energy storage DC/DC converter is switched to a constant direct current voltage control mode to maintain the power balance of the system and control the voltage of the direct current bus, but the power regulation margin of the energy storage unit is possibly exceeded under the condition, if the power regulation margin of the energy storage unit is exceeded, the energy storage unit enters a current limiting mode and operates by maximum power discharge, at the moment, the voltage of the direct current bus continuously drops, and when the voltage drops to 0.95% of the voltage instruction value of the direct current bus, the control mode of the converter is switched to constant direct current voltage control; after the fault is eliminated, the power command of each port is adjusted by the power grid dispatching to enable the system to be recovered to the first operation condition;
step four: when the system is regulated and is in the state that the fluctuation quantity of the direct current bus voltage is less than or equal to 1% of the direct current bus voltage instruction value again from other working conditions, secondary regulation is carried out on the energy storage DC/DC converter; the time required by the energy storage DC/DC converter for secondary regulation is more than or equal to Tmin，TminComprises the following steps:
wherein, PessWhen the system re-enters the direct current bus voltage fluctuation amount from other working conditions through dynamic adjustment and is less than or equal to 1% of the direct current bus voltage instruction value, the transmission power still maintained by the energy storage DC/DC converter is realized, delta t is the time required by the main converter to respond to the system power change, C is the system direct current bus capacitor, and delta U is the time required by the main converter to respond to the system power changedc.maxThe maximum value of the difference of the voltage changes of the direct current bus.
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