CN111342494A - Energy storage converter communication-line-free parallel connection strategy based on bus voltage event detection - Google Patents

Abstract

The invention discloses an energy storage converter communication-line-free parallel strategy based on bus voltage event detection, which is based on the background that the distance between the load ends of the energy storage converters is close, realizes the power equalization of each energy storage converter by acquiring a voltage signal of a public end of a PCC point as a public event signal and based on a PCC voltage feedback method, and utilizes the event signal of the PCC voltage as a synchronous signal for realizing the voltage frequency recovery of each energy storage converter based on the principle of an event detection mechanism, thereby avoiding the requirement of each energy storage converter on communication interconnecting lines. The strategy control method is simple and practical, convenient to improve, good in system expansibility, low in construction cost of the multi-machine parallel system without the interconnection line and relatively practical in engineering application value.

Description

Parallel strategy of energy storage converter without communication line based on bus voltage event detection

technical field

The invention belongs to the technical field of energy storage converter control, and in particular relates to a non-communication line parallel connection strategy of energy storage converters based on bus voltage event detection.

Background technique

The disadvantages of traditional fossil energy have led to the rapid development of related research on new energy. Distributed power sources such as new energy have small power generation capacity and usually need parallel power supply. hot spot. The droop control is often used in the parallel connection of multiple energy storage converters. Due to the droop characteristics, problems such as power distribution and voltage and frequency recovery are usually faced. Under the inductive line impedance, the distribution of active power will be automatically divided according to the droop coefficient. The distribution will be affected by the line impedance. When the line impedance is inconsistent, the reactive power output of the energy storage converter will be uneven.

Under the inductive line impedance, the traditional active-frequency and reactive-voltage droop control is used, and the voltage and frequency will shift with the change of the load power. The usual method is to detect the output voltage of the energy storage converter in real time and The frequency is compared with the rated value, and then the voltage and frequency deviation of each energy storage converter are synchronously compensated to each energy storage converter. Through the PI controller, the final output value of the energy storage converter will be stable. at rated value. This method requires mutual communication between the energy storage converters to achieve synchronous compensation. When the compensation is not synchronized, the output error of the energy storage converters will accumulate, which will eventually lead to the instability and collapse of the parallel system of the energy storage converters. A communication line is required between the power converters to achieve synchronization. However, the use of communication lines will increase the complexity of the system, especially when the number of parallel units increases, it will reduce the stability of the system.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a parallel strategy of energy storage converters without communication lines based on bus voltage event detection. In this way, the power sharing of each energy storage converter and the synchronous secondary recovery of voltage and frequency are realized.

In order to achieve the above purpose, the present invention provides a parallel strategy for energy storage converters without communication lines based on bus voltage event detection, including a power sharing strategy and a voltage frequency recovery strategy,

1) The power sharing strategy includes the following steps:

1.1. Sampling the bus voltage V _PCC of the PCC point;

1.2. Measure the real-time reactive power Q _it output by the ith energy storage converter, and use the reactive power Q _it output by the ith energy storage converter to calculate the command voltage V _refi after droop control,

1.3. Integrate the deviation between the bus voltage V _PCC of the energy storage converter PCC and the command voltage V _ref1 after droop control, and the integration result E ₁ is used as the actual output voltage of the energy storage converter;

是第i台储能变流器的额定电压，D_qi是第i台储能变流器的下垂系数；1.4. Under the condition of V _refi =V _PCC , the expression for the output reactive power Q _i of the i-th energy storage converter when it is stable is:

is the rated voltage of the i-th energy storage converter, and D _qi is the droop coefficient of the i-th energy storage converter;

1.5. If the rated voltages of all the energy storage converters running in parallel are equal, and the droop coefficients are equal, the output reactive power of all energy storage converters can be equal;

2) The voltage frequency recovery strategy includes the following steps:

2.1. Sampling PCC point bus voltage frequency;

2.2. An event detection mechanism is established based on the PCC voltage and frequency information, and the event signal is used as a unified synchronization signal for the secondary compensation of each energy storage converter;

2.3. Measure the actual output voltage V of the energy storage converter and the actual output frequency ω, calculate the deviation between the output voltage of the energy storage converter and the rated value (V ₀ -V), and calculate the deviation between the frequency and the rated value (ω ₀ -ω), where V ₀ is the rated voltage of the energy storage converter, and ω ₀ is the rated frequency of the energy storage converter;

2.4. Wait for the secondary compensation synchronization event signal, if there is no secondary compensation event signal, repeat steps 2.1 to 2.3, otherwise go to step 2.5;

2.5. When the event signal is triggered, each energy storage converter superimposes the voltage compensation value δV on the actual output voltage V of the energy storage converter, and superimposes the frequency compensation value δω on the actual output frequency ω of the energy storage converter to achieve Synchronous voltage frequency recovery.

Further, in step 2.2, the frequency offset of the PCC busbar voltage exceeds 0.02 Hz as the event signal of the secondary compensation synchronous action of each energy storage converter.

是第i台储能变流器的额定电压，D_qi是第i台储能变流器的下垂系数。Further, in step 1.2, the reactive voltage droop relationship is as follows

is the rated voltage of the i-th energy storage converter, and D _qi is the droop coefficient of the i-th energy storage converter.

k_qi是第i台储能变流器的积分器参数。Further, in step 1.2, the expression of the actual output voltage E _i of the energy storage converter is:

k _qi is the integrator parameter of the ith energy storage converter.

Further, when the secondary compensation event signal occurs, step 2.5 is performed after the dynamic adjustment process of the parallel system is completed.

Further, in step 2.5, the calculation formula of δV of the secondary voltage amplitude is: δV=k _pV (V ₀ -V)+k _iV ∫(V ₀ -V)dt, where k _pV is the proportional coefficient of the voltage compensation value, k _iV is the integral coefficient of the voltage compensation value.

Further, in step 2.5, the calculation formula of the compensation value δω of the secondary voltage frequency recovery is: δω=k _pf (ω ₀ -ω)+k _if ∫(ω ₀ -ω)dt, k _pf is the frequency compensation value ratio coefficient, k _if is the integral coefficient of frequency compensation value.

Further, in step 2.5, when using the PCC bus voltage zero-crossing signal to perform step recovery improvement, the frequency compensation value δω is a recovery step size, and a recovery step size is 0.005H _Z -0.1H _Z to achieve voltage frequency recovery.

Compared with the prior art, the present invention has at least the following beneficial technical effects:

The control strategy is based on the background of the close distance between the load terminals of the energy storage converters. By obtaining the PCC bus voltage signal as the common event signal of each energy storage converter, and based on the event detection principle, the event signal of the PCC voltage is used as each energy storage converter. The current converter realizes the synchronous action signal of voltage and frequency recovery, thereby avoiding the requirement for the communication interconnection between the energy storage converters.

Each energy storage converter obtains the PCC bus voltage signal, and based on the PCC voltage feedback method, the problem of power equalization of the energy storage converter in parallel without interconnection lines is solved. Using the PCC bus voltage, the power sharing and voltage frequency recovery of the energy storage converter when the energy storage converter is running off-grid without interconnection lines is realized. The whole system has good control performance. By collecting PCC bus information, it is used to solve the problems of power sharing and voltage frequency recovery, which saves the construction cost of interconnecting lines between energy storage converters.

For the secondary recovery of voltage and frequency, in view of the disadvantage that the traditional method requires communication lines to achieve synchronization compensation, the event signal of the PCC bus voltage is used as the synchronization signal to achieve secondary recovery. The control method is simple and easy to implement, easy to improve and upgrade, does not require interconnected communication lines, is economical, improves system stability, and has a simple and easy-to-implement control structure, which has practical engineering application value.

For the power sharing problem, the PCC voltage feedback method is adopted, and the PCC bus voltage is used as a unified reference potential to realize the power distribution. As a feasible power sharing strategy, the PCC voltage feedback method has the advantages of simple and easy control, fast response speed, etc., and does not need to obtain the power information of other energy storage converters. The PCC bus voltage is sampled in real time and fed back to the reference command of the droop control. The response speed is fast and will not affect the power quality of the original circuit.

Description of drawings

Fig. 1 is the control principle diagram of the non-communication line parallel connection strategy of the energy storage converter based on the bus voltage event detection introduced by the present invention;

Fig. 2 is the control block diagram of the PCC voltage feedback method introduced by the present invention;

Fig. 3 is the principle analysis diagram of the PCC voltage feedback method introduced by the present invention;

4a is a schematic diagram of the secondary frequency recovery introduced by the present invention;

4b is a schematic diagram of the secondary voltage recovery introduced by the present invention;

Fig. 5a is the frequency recovery control block diagram based on the event detection signal introduced by the present invention;

Fig. 5b is the voltage recovery control block diagram based on the event detection signal introduced by the present invention;

6a is a waveform diagram of the active power of the energy storage converter in the simulation waveform of the non-communication line paralleling strategy based on bus voltage event detection of the energy storage converter introduced by the present invention;

Fig. 6b is the energy storage converter reactive power waveform diagram in the simulation waveform of the non-communication line paralleling strategy based on bus voltage event detection of the energy storage converter introduced by the present invention;

6c is a waveform diagram of the output frequency of the energy storage converter in the simulation waveform of the non-communication line paralleling strategy based on the bus voltage event detection of the energy storage converter introduced by the present invention;

FIG. 6d is a waveform diagram of the output voltage amplitude of the energy storage converter in the simulation waveform of the non-communication line paralleling strategy based on bus voltage event detection of the energy storage converter introduced in the present invention;

Fig. 7a is a frequency secondary step recovery diagram;

Fig. 7b is a partial enlarged view of Fig. 7a;

Figure 7c is a graph of the output active power of the step recovery converter.

Detailed ways

In order to make the purpose and technical solutions of the present invention clearer and easier to understand. The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Below, the present invention will be described from two aspects of power sharing and voltage frequency recovery:

1) Power sharing strategy:

The control principle diagram of the multi-machine parallel system of energy storage converters without interconnection line is shown in Figure 1. There is no interconnection communication line between energy storage converters, and the distance between the load ends is relatively close. On the one hand, considering that the power supply load is far from the energy storage converter On the other hand, the output of the energy storage converter is filtered by LCL, and the line impedance can be ignored compared with the filter inductance L. Therefore, it is approximately considered that the filter inductance L is the output impedance of the energy storage converter. The droop control is used to realize the multi-machine parallel connection of energy storage converters without interconnection lines. The inductive part X of the line impedance is much larger than the resistive part R, so the output impedance is inductive, so the droop control can use traditional active-frequency, reactive-voltage droop control, and the specific control relationship is as follows:

In the above formula, ω _rated is the rated frequency output by the energy storage converter, E _rated is the rated voltage output by the energy storage converter, P _rated is the rated active power output by the energy storage converter, and Q _rated is the energy storage converter output. is the rated reactive power output by the converter, m _P is the droop coefficient of active power, n _Q is the droop coefficient of reactive power, P _i is the actual output active power of the i-th energy storage converter, and Q _i is the i-th energy storage converter. The actual output reactive power of the energy storage converter, ω _i is the actual output frequency of the ith energy storage converter, and E _i is the actual output voltage of the ith energy storage converter.

Under the inductive line impedance, the active and reactive power output of a single unit when the energy storage converters are operated in parallel are:

In the above formula, E _i is the actual output voltage of the ith energy storage converter, V _PCC is the bus voltage of the parallel system, δ _i is the phase angle between the output voltage of the ith energy storage converter and the bus voltage The difference, (X _Zi +X _Li ) is the output impedance of the line where the ith energy storage converter is located, where X _Zi is the line impedance value of the line where the ith energy storage converter is located, and X _Li is the line impedance value of the ith energy storage converter. The inductance impedance value of the line where the energy converter is located.

Existing studies have shown that under the condition of inductive line impedance, the active power distribution of the energy storage converter can be evenly divided when it is stable, while the reactive power distribution is affected by the line impedance. When the line impedance is inconsistent, the reactive power cannot be Achieving an equal share, therefore measures need to be taken to achieve an equal share of reactive power.

Under the background that the energy storage converter has no interconnection lines and multiple machines in parallel, the method with communication conditions cannot be used, and the extremely small line impedance is ignored, so the voltage drop on the line impedance can also be ignored. The energy storage converter LCL The output voltage can be approximated to the PCC bus voltage, and the PCC bus voltage can be measured in engineering, and finally the PCC voltage method is used to realize the reactive power equalization.

是储能变流器的额定参考电压，V_ref1是经过下垂控制后的指令电压，D_q1是储能变流器的下垂系数，将储能变流器PCC母线电压V_PCC反馈回来与下垂控制后的指令电压V_ref1做比较，将两者的偏差做积分，积分结果E₁作为储能变流器的实际输出电压。详细的原理分析如图3：The principle of PCC voltage feedback method is to provide a unified reference potential to realize the problem of reactive power distribution. Its specific structural block diagram is shown in Figure 2.

is the rated reference voltage of the energy storage converter, V _ref1 is the command voltage after droop control, D _q1 is the droop coefficient of the energy storage converter, and the energy storage converter PCC bus voltage V _PCC is fed back to the droop control. The latter command voltage V _ref1 is compared, and the deviation of the two is integrated, and the integration result E ₁ is used as the actual output voltage of the energy storage converter. The detailed principle analysis is shown in Figure 3:

When the line impedance values of the two energy storage converters are inconsistent, uneven reactive power will occur. In Figure 3, point A represents the reactive power of energy storage converter A when the system voltage is stable, and point B represents the reactive power of energy storage converter A when the system voltage is stable. When the system voltage is stable, the corresponding reactive power of the energy storage converter B, the line impedance value of the energy storage converter A is larger than the line impedance value of the energy storage converter B, and the energy storage converter A can be obtained from the figure The output reactive power is small, and the output voltage value of the corresponding energy storage converter A is higher. When the PCC voltage feedback method is added, the actual output voltage of the energy storage converter becomes the integral of the command voltage V _ref1 after droop control and the difference between the PCC voltage, that is, the integral of ΔE _a and ΔE _b . The line impedance of converter A is large. It can be seen from Figure 3 that the output voltage of energy storage converter A is higher, and its corresponding ΔE _a is also larger, so the integral value of ΔE _a after PCC voltage feedback is also larger, That is, the output voltage of the energy storage converter A is increased, thereby increasing the reactive power output by the energy storage converter A. After continuous feedback and adjustment, the output reactive power of energy storage converter A continues to increase. When the parallel system reaches stability, the output reactive power of energy storage converter A and energy storage converter B are equal. The active power can be automatically equally divided under the inductive line impedance, thus solving the problem of power distribution.

The feasibility of the PCC voltage feedback method is deduced from a theoretical point of view as shown in Figure 2:

For energy storage converter A there are:

是储能变流器A的额定电压，V_ref1是经过下垂控制后的指令电压，D_q1是储能变流器A的下垂系数，Q₁是储能变流器A的输出无功功率，V_PCC是PCC母线电压，k_q1是储能变流器A的积分器参数。In the above formula, E ₁ is the actual output voltage of the energy storage converter A,

is the rated voltage of the energy storage converter A, V _ref1 is the command voltage after droop control, D _q1 is the droop coefficient of the energy storage converter A, Q ₁ is the output reactive power of the energy storage converter A, V _PCC is the PCC bus voltage, and k _q1 is the integrator parameter of the energy storage converter A.

In the same way, for the energy storage converter B:

是储能变流器B的额定电压，V_ref2是经过下垂控制后的指令电压，D_q2是储能变流器B的下垂系数，Q₂是储能变流器B的输出无功功率，V_PCC是PCC母线电压，k_q2是储能变流器B的积分器参数。In the above formula, E ₂ is the actual output voltage of the energy storage converter B,

is the rated voltage of the energy storage converter B, V _ref2 is the command voltage after droop control, D _q2 is the droop coefficient of the energy storage converter B, Q ₂ is the output reactive power of the energy storage converter B, V _PCC is the PCC bus voltage, and k _q2 is the integrator parameter of the energy storage converter B.

When the steady state is reached, the output voltage of the energy storage converter remains stable, and the input of the integrator is 0, thus:

In the above formula, V _ref1 is the command voltage of the energy storage converter A, V _ref2 is the command voltage of the energy storage converter B, and V _PCC is the PCC bus voltage.

Substituting the above equations into the corresponding droop equations of each energy storage converter, we can get:

分别是储能变流器A和储能变流器B的额定电压，V_PCC是PCC母线电压，D_q1,D_q2分别是储能变流器A和储能变流器B的下垂系数In the above formula, Q ₁ and Q ₂ are the output reactive power of energy storage converter A and energy storage converter B, respectively,

are the rated voltages of energy storage converter A and energy storage converter B, respectively, V _PCC is the PCC bus voltage, D _q1 , D _q2 are the droop coefficients of energy storage converter A and energy storage converter B, respectively

以及下垂系数D_q1＝D_q2，则有Q₁＝Q₂，即实现了采用PCC电压反馈法解决无功功率均分问题。Let the rated voltage of energy storage converter A and energy storage converter B

And the droop coefficient D _q1 =D _q2 , then Q ₁ =Q ₂ , that is, the PCC voltage feedback method is used to solve the problem of reactive power sharing.

2) Voltage frequency recovery:

The droop control of the energy storage converter can realize the approximate power distribution and the stability of the voltage and frequency without interconnecting wires. The power distribution error can be corrected by the above PCC voltage feedback method, and the voltage or frequency caused by the droop control The offset needs to be recovered by secondary control.

For a single energy storage converter, the influence of its droop control is as follows:

Among them, ω is the actual output frequency of the energy storage converter, V is the actual output voltage of the energy storage converter; ω ₀ is the rated frequency of a single energy storage converter, and V ₀ is the rated frequency of a single energy storage converter voltage, P is the actual output active power of a single energy storage converter, Q is the actual output reactive power of a single energy storage converter, m is the droop coefficient of active frequency, and n is the droop coefficient of reactive power. From formula 1.7, it can be concluded that different output powers (output active power - output reactive power) make the voltage and frequency offsets of the energy storage converters different, so it is necessary to compensate each energy storage converter through secondary adjustment. Its own offset, the compensation method is to superimpose a compensation value on the basis of the original droop control:

in:

In the above formula, k _pV is the proportional coefficient of the voltage compensation value, k _iV is the integral coefficient of the voltage compensation value; k _pf is the proportional coefficient of the frequency compensation value, and k _if is the integral coefficient of the frequency compensation value.

When the secondary compensation is implemented, the energy storage converter measures its own output voltage and frequency in real time, compares it with the rated value set by itself, and integrates the difference through PI to obtain the real-time frequency compensation value δω and voltage compensation value δV , when the parallel system is stable, there are ω ₀ =ω, V ₀ =V. After the droop control is compensated twice, the voltage amplitude and frequency can be restored to the rated value. The specific effects are shown in Figure 4a and Figure 4b:

As shown in the schematic diagram of the secondary frequency recovery in Figure 4a, the primary control adopts droop control, resulting in the stable state of the energy storage converter at point a. At this time, the output frequency is ω, and there is a frequency offset. After secondary control, on the basis of the original primary control Compensate for a δω value, the stable state of the energy storage converter is point b, and the output frequency is the rated value ω ₀ at this time to achieve frequency recovery; similarly, as shown in the schematic diagram of secondary voltage recovery in Figure 4b, the primary control adopts droop control, resulting in storage The stable state of the energy converter is point a, and the output voltage is V at this time, and there is a voltage offset. After secondary control, a δV value is compensated on the basis of the original primary control, and the stable state of the energy storage converter is point b. At this time The output voltage is at the rated value V ₀ for voltage recovery. The compensation method of secondary control is simple and easy to implement, but the problem is how to solve the compensation synchronization problem. When the compensation is not synchronized, the error will accumulate with the increase of the compensation times, resulting in an increasing power distribution deviation, which will eventually lead to multiple machines. When the parallel system collapses, the existing solution is to use the central controller to communicate with each energy storage converter, and the central controller sends a unified compensation signal when compensation is required; another solution is to use the energy storage converter to In the case of weak communication, consistency theory such as graph theory is used to achieve secondary compensation and reduce communication costs. In order to realize the secondary recovery synchronization problem without interconnecting communication lines, the present invention adopts an event detection mechanism to provide a unified synchronization compensation signal.

Each energy storage converter can obtain the PCC bus voltage information. Therefore, the PCC bus information is used as the unified event signal of the multi-machine parallel system of energy storage converters. The event is triggered when the frequency shift of the PCC voltage and frequency exceeds the specified value. The specific process is that the energy storage converter detects the PCC bus voltage and frequency information in real time. When the frequency deviation is within the specified range, the event signal is not triggered, and the multi-machine parallel system of the energy storage converter is maintained stable by droop control; When the specified range is exceeded, the event signal is triggered, and each energy storage converter receives a unified event signal. After a certain delay to avoid the dynamic adjustment process, the voltage and frequency are compensated twice on the basis of droop control to restore to the rated value. and repeat the process. The control principle diagram is shown in Figure 5:

As shown in Figure 5a, based on the frequency recovery control block diagram of the event detection signal, the frequency deviation (ω ₀ -ω) is calculated. When the event signal is triggered, the dynamic adjustment process is avoided through the delay link, and the deviation value can be obtained through the PI controller. The compensation value δω, The frequency compensation value is superimposed on the active power-frequency droop control to realize frequency recovery. Similarly, as shown in Figure 5b, the voltage recovery control block diagram based on the event detection signal is used to calculate the voltage deviation (V ₀ -V). When the event signal is triggered, after the delay In the time link, the compensation value δV can be obtained through the PI controller, and the voltage compensation value can be superimposed on the reactive power-voltage droop control to achieve voltage recovery;

A parallel strategy of energy storage converter without communication line based on bus voltage event detection includes two parts: power sharing strategy and voltage frequency recovery strategy.

1. Power sharing strategy - PCC voltage feedback method:

1.1. Sampling PCC point bus voltage information;

是储能变流器A的额定电压，D_q1是储能变流器A的下垂系数，得到经过下垂控制后的指令电压V_ref1。1.2. Measure the output voltage and output current of the energy storage converter, take the power sharing control block diagram of the energy storage converter A as an example, as shown in Figure 2, measure the real-time reactive power Q _1t output by the energy storage converter, And construct the reactive voltage droop relationship

is the rated voltage of the energy storage converter A, D _q1 is the droop coefficient of the energy storage converter A, and the command voltage V _ref1 after the droop control is obtained.

1.3. Feed back the PCC bus voltage V _PCC of the energy storage converter and compare it with the command voltage V _ref1 after droop control, and integrate the deviation between the two, that is, E ₁ =k _q1 ∫(V _ref1 -V _PCC )dt , k _q1 is the integrator parameter, and the integration result E ₁ is the actual output voltage of the energy storage converter;

可计算得储能变流器A输出无功功率稳定时的无功功率

1.4. Under the action of the integrator, there is V _ref1 =V _PCC when it is stable, and then combined with the reactive voltage droop relationship

The reactive power when the output reactive power of the energy storage converter A is stable can be calculated

是储能变流器B的额定电压，D_q2是储能变流器B的下垂系数。1.5. The same control strategy is implemented for energy storage converter B. When it is stable, the output reactive power of energy storage converter B can be obtained as

is the rated voltage of the energy storage converter B, and D _q2 is the droop coefficient of the energy storage converter B.

以及下垂系数D_q1＝D_q2，则有Q₁＝Q₂，实现了采用PCC电压反馈法解决无功功率均分问题。1.6. Set the rated voltage of energy storage converter A and energy storage converter B

And the droop coefficient D _q1 =D _q2 , then there is Q ₁ =Q ₂ , which realizes the use of the PCC voltage feedback method to solve the problem of reactive power equalization.

2. Voltage and frequency recovery strategy - secondary compensation strategy based on event detection

2.1. Sampling PCC point bus voltage and frequency information;

2.2. The event detection mechanism is established based on the PCC voltage and frequency information, and the PCC bus voltage frequency deviation exceeding 0.02Hz is used as the event signal, and the event signal is used as the unified synchronization signal for the secondary compensation of each energy storage converter;

2.3. Measure the actual output voltage V and frequency ω of the energy storage converter, and calculate the deviation values (V ₀ -V) and (ω ₀ -ω) of the output voltage and frequency of the energy storage converter from the rated value respectively, where V ₀ and ω ₀ are rated voltage and rated frequency, respectively;

2.4. Wait for the event signal of secondary compensation, if there is no event signal, repeat the above steps;

2.5. When the event signal occurs, the dynamic adjustment process is avoided through the same delay link, PI integration is performed on the voltage and frequency deviation values, and the compensation values δV and δω for the secondary voltage and frequency recovery are obtained respectively, as shown in formula (1.9).

2.6. The voltage and frequency compensation values δV, δω are superimposed on the corresponding droop control according to the synchronization signal to realize the voltage and frequency recovery.

The invention proposes a parallel strategy of energy storage converters without communication lines based on bus voltage event detection. The MTALB+PLECS software platform is used to build an off-grid multi-machine parallel system platform for energy storage converters without interconnection lines. The control scheme and related algorithms are simulated and verified, which proves the correctness and reliability of the method.

The simulation results are shown in Figures 6a to 6d. Loads are applied at t=4s and t=10s. In Figures 6a to 6d, gray represents energy storage converter A, and black represents energy storage converter B.

It can be seen from Figure 6a that the active power of the energy storage converter is loaded at t=4s and t=10s respectively, the output active power of the two energy storage converters increases, and the active power can be shared equally;

It can be seen from Figure 6b that the reactive power of the energy storage converter is loaded at t=4s and t=10s respectively, the output reactive power of the two energy storage converters increases, and the reactive power can be shared equally;

It can be seen from Figure 6c that when the output frequency of the energy storage converter is at t=4s, the frequency deviates from the rated value by 50Hz and exceeds 0.02Hz, the synchronization event is triggered, the energy storage converter starts secondary recovery, and the frequency of the energy storage converter is restored to Rated value, when t=10s, the secondary recovery process starts again, so that the output frequency of the energy storage converter is stabilized at 50Hz again.

It can be seen from Figure 6d that when the voltage amplitude of the PCC bus of the energy storage converter is at t=4s, the synchronization event is triggered, the energy storage converter starts the secondary recovery, and the voltage amplitude of the energy storage converter of the PCC bus is restored to the rated value. 314V, when t=10s, the secondary recovery process starts again, and the final PCC bus voltage amplitude stabilizes at 314V.

It can be seen from the simulation results that this method can well realize the power sharing and voltage frequency recovery problems of energy storage converters without interconnecting lines and off-grid multi-machine parallel systems. The strategy of "parallel strategy for converters without communication lines" has excellent performance, high reliability and easy implementation, and provides a high reference value for the power sharing and voltage frequency recovery problems of energy storage converters without interconnection lines and off-grid multi-machine parallel systems. .

In the secondary recovery process, since the continuous PI recovery link has major problems in introducing errors and implementation difficulties, a discrete step recovery process can be used for further improvement. Taking the secondary recovery of the frequency of the energy storage converter as an example, Each energy storage converter measures the zero-crossing point of the PCC bus voltage. At each zero-crossing point, a frequency recovery step is superimposed on the output frequency of the energy storage converter, and each energy storage converter performs a synchronous frequency step. Recovery, when the frequency offset is less than the allowable offset value, stop the recovery process. The event signal is also used as the synchronization signal for the unified compensation of each energy storage converter. In this way, after a certain time step accumulation, the output frequency of the energy storage converter can be restored to the vicinity of the rated value, and a discrete step recovery improvement strategy is adopted. The accumulation of errors caused by the continuous adjustment process can be reduced. Taking the frequency adjustment of the energy storage converter as an example, a simulation is built on the MATLAB+despace software platform to verify the strategy. The simulation results are shown in Figure 7a to Figure 7c. In Fig. 7a to Fig. 7c, gray represents the energy storage converter A, and black represents the energy storage converter B. As can be seen from Figure 7a and Figure 7b, when t=3s, the loading causes the frequency offset to exceed the specified range, and the event signal is triggered. The output frequency of the converter is restored in stages according to the PCC zero-crossing signal. At the end, the output frequency of the energy storage converter can be stabilized around the rated value of 50Hz, which can achieve a good secondary frequency recovery effect, and reduce the accumulation of errors and the difficulty of engineering realization. . It can be seen from Figure 7c that in the process of frequency recovery, the active power sharing is not affected. Similarly, a similar improvement strategy can be used for the voltage recovery strategy.

The strategy control method is simple and practical, easy to improve, and has good system expansibility.

The above content is a further detailed description of the present invention in conjunction with the specific preferred embodiments, and it cannot be considered that the specific embodiments of the present invention are limited to this. Below, some simple deductions or substitutions can also be made, all of which should be regarded as belonging to the invention and the scope of patent protection determined by the submitted claims.

Claims (8)

1. A communication-line-free parallel strategy for an energy storage converter based on bus voltage event detection is characterized by comprising a power equalization strategy and a voltage frequency recovery strategy,

1) the power sharing strategy comprises the following steps:

1.1, sampling the bus voltage V of the PCC point_PCC；

1.2, measuring the real-time reactive power Q output by the ith energy storage converter_itAnd utilizes the reactive power Q output by the ith energy storage converter_itCalculating the command voltage V after droop control_refi，

1.3, generating line voltage V of PCC of energy storage converter_PCCAnd the command voltage V after droop control_ref1The deviation of (a) is integrated, the result of the integration E₁As the actual output voltage of the energy storage converter;

1.4 at V_refi＝V_PCCObtaining the output reactive power Q when the ith energy storage converter is stable_iThe expression of (a) is:

rated voltage of ith energy storage converter, D_qiThe droop coefficient of the ith energy storage converter is obtained;

1.5, setting the rated voltages of all the energy storage converters running in parallel to be equal and the droop coefficients to be equal, so that the output reactive powers of all the energy storage converters can be equal;

2) the voltage frequency recovery strategy comprises the following steps:

2.1, sampling the voltage frequency of a PCC point bus;

2.2, establishing an event detection mechanism by using the PCC voltage frequency information, wherein an event signal is used as a synchronous signal for secondary compensation unification of each energy storage converter;

2.3, measuring the actual output voltage V and the actual output frequency omega of the energy storage converter, and calculating the deviation value (V) of the output voltage and the rated value of the energy storage converter₀V) calculating a deviation value (omega) of the frequency from a nominal value₀ω) wherein V₀For rated voltage, omega, of energy-storing converters₀The rated frequency of the energy storage converter;

2.4, waiting for a secondary compensation synchronous event signal, if no secondary compensation event signal exists, repeating the step 2.1 to the step 2.3, otherwise, performing the step 2.5;

and 2.5, when the event signal is triggered, each energy storage converter superposes the voltage compensation value delta V on the actual output voltage V of the energy storage converter, and superposes the frequency compensation value delta omega on the actual output frequency omega of the energy storage converter, so that the synchronous voltage frequency recovery is realized.

2. The energy storage converter communication-line-free parallel strategy based on bus voltage event detection according to claim 1, wherein in step 2.2, PCC bus voltage frequency deviation exceeding 0.02Hz is used as an event signal for secondary compensation synchronous action of each energy storage converter.

3. The energy storage converter communication-line-less parallel strategy based on bus voltage event detection as claimed in claim 1, wherein in step 1.2, the reactive voltage droop relation is

Rated voltage of ith energy storage converter, D_qiAnd the droop coefficient of the ith energy storage current transformer is shown.

4. The communication-line-less parallel strategy for energy storage converters based on bus voltage event detection as claimed in claim 1, wherein in step 1.2, the actual output voltage E of the energy storage converter_iThe expression of (a) is: e_i＝k_qi∫(V_refi-V_PCC)dt，k_qiIs the integrator parameter of the ith energy storage current transformer.

5. The communication-line-less parallel strategy for the energy storage converters based on bus voltage event detection as claimed in claim 1, wherein when the secondary compensation event signal occurs, the dynamic adjustment process of the parallel system is completed and then step 2.5 is performed.

6. A method as claimed in claim 1The energy storage converter communication-line-free parallel strategy based on bus voltage event detection is characterized in that in the step 2.5, a calculation formula of delta V of a secondary voltage amplitude is as follows: δ V ═ k_pV(V₀-V)+k_iV∫(V₀-V)dt，k_pVIs a voltage compensation value proportionality coefficient, k_iVIs the voltage compensation value integral coefficient.

7. The energy storage converter communication-line-less parallel strategy based on bus voltage event detection as claimed in claim 1, wherein in step 2.5, the compensation value δ ω for secondary voltage frequency recovery is calculated by the formula: δ ω ═ k_pf(ω₀-ω)+k_if∫(ω₀-ω)dt，k_pfAs a frequency compensation value proportional coefficient, k_ifIs the frequency compensation value integral coefficient.

8. A communication-line-less parallel strategy for energy storage converters based on bus-bar voltage event detection according to claim 1, wherein in step 2.5, when step recovery improvement is performed by using PCC bus-bar voltage zero crossing signal, the frequency compensation value δ ω is a recovery step, and one recovery step is 0.005H_Z-0.1H_ZAnd voltage frequency recovery is realized.

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