A virtual inertia coordinated control method for multi-port intelligent power electronic device

Abstract

The application provides a virtual inertia coordination control method of a multi-port intelligent power electronic device, which comprises the following steps: 1. proposing a DC bus system control strategy through an AC bus system control strategy; 2. changing the DC bus voltage, and the relevant port converter works to stabilize the DC bus voltage; and 3. judging the working state of the port converter through the bus voltage change rate according to the working state of each port converter, and the system runs in different working conditions. The application can compensate energy for the DC system all day long, and plays an important role in maintaining the stability of the DC bus voltage.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation and converter current control, and mainly relates to a virtual inertial coordination control method for multi-port intelligent power electronic equipment. Background Technology

[0002] In recent decades, to reduce reliance on traditional fossil fuels, the development of new energy power generation such as wind and solar power has accelerated. To address the challenges of new energy power generation, the concept of "energy interconnection" was proposed. As a key component of "energy interconnection," the energy router naturally attracts considerable attention, and DC bus power balance is a primary criterion for evaluating the stability of the energy router system. Studying the stability of an energy router system mainly involves examining whether the DC bus power can maintain balance, and the most direct indicator of balance is the stability of the DC bus voltage. New energy sources such as wind and solar power account for a large proportion of distributed generation, resulting in low inertia in the generators of these new energy sources. Low inertia makes the DC bus voltage highly susceptible to external fluctuations, leading to voltage drops and surges. In DC grid systems, distributed generation units and loads are generally connected to the DC bus via power electronic converters. However, due to the lack of inertia, converter-dominated DC networks make the DC bus voltage extremely sensitive to power fluctuations from micro-sources and loads, severely impacting the system's power quality and safe, stable operation. To address the low inertia problem of DC systems, virtual inertial control, which aims to reduce the rate of change of DC voltage and thus suppress DC bus voltage fluctuations, has gradually become a research hotspot in the field of DC grid technology. Currently, most research on virtual inertia focuses on single converter control strategies, without considering the impact of applying inertial strategies on the stability of the entire system. However, the negative damping characteristics of constant power loads and the interactions between converters in DC grid systems can affect the overall stability of multi-port systems, and may even lead to oscillations and instability. To date, there is no research on a reasonable way to coordinate the inertia of various generation units and related loads to address the low inertia and low damping characteristics of DC systems. Summary of the Invention

[0003] To achieve multi-energy complementarity and inertial allocation between the power generation ports and load ports, this invention proposes a virtual inertial coordination control method for multi-port intelligent power electronic devices.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A virtual inertial coordinated control method for multi-port intelligent power electronic devices includes the following steps:

[0006] Step 1. Propose a control strategy for the DC bus system based on the control strategy for the AC bus system;

[0007] Step 2. Determine the operating status of the port converter by measuring the bus voltage change rate;

[0008] Step 3. The system operates under different conditions based on the working status of each port converter.

[0009] Further, step 1 includes converting the synchronous generator control equations in the AC bus system into virtual inertial control equations in the DC system;

[0010] The control equations for the synchronous generator in the AC bus system are:

[0011]

[0012] In the formula, ω n The rated angular frequency of the common bus; t is time, dω / dt is the rate of change of the angular frequency; P M P is the mechanical power input to the motor. E H is the electromagnetic power output of the motor; H is the damping coefficient; J is the virtual moment of inertia.

[0013] The virtual inertial control equations in the converted DC system are as follows:

[0014]

[0015] In the formula, i dc U is the current on the DC side of the power grid. dc_ref K is the reference value for the DC side voltage of the power grid. G U is the droop coefficient of the G-VSC droop control curve; dc C is the DC bus voltage; v This is the virtual capacitance value; dU dc / dt is the rate of change of the DC bus voltage; i dc_ref This is the reference value for the DC bus voltage;

[0016] Further, step 2 includes:

[0017] Real-time monitoring of DC bus voltage change rate dU dc / dt and the battery charge SOC are expressed through the absolute value of the rate of change of the DC bus voltage |dU dc The value of / dt| is compared with the steady-state limit value δ set by the system, and it is determined whether the battery charge is at the working charge level. Based on the specific comparison, the value of the virtual capacitor required by the DC bus system is calculated, and the inertia of the DC system is provided by charging and discharging the virtual capacitor.

[0018] Furthermore, the formula for the virtual capacitance includes:

[0019] (1) Absolute value of DC bus voltage change rate |dU dcWhen dt| < δ, the system is in steady state. When the DC bus system is in steady state, the total system energy input power equals the load power used, i.e.:

[0020] P pv +P wind =P Load

[0021] At this point, the system power is balanced, and neither the energy storage port converter nor the grid-connected port converter participates in operation. The virtual capacitance value required when the system DC bus voltage equals the set value is the steady-state system virtual capacitance value.

[0022] C v =C1

[0023] Where C1 is the virtual capacitance value of the system in steady state;

[0024] (2) Absolute value of DC bus voltage change rate |dU dc When |dt|≥δ, the system is in an unsteady state; if the battery charge is at its working charge, i.e., SOC... min <SOC<SOC max At this time, the energy storage port converter and the grid-connected port converter operate simultaneously. When the multi-port equipment is in an unsteady state, the total system energy input power is not equal to the load power. If the battery charge is within the normal charge range, and the grid-connected port converter and the energy storage port converter operate simultaneously, the main grid and the battery are equivalent to a virtual capacitor. The inertia of the system is increased by charging and discharging the virtual capacitor. At this time, the value of the virtual capacitor is:

[0025]

[0026] In the formula, C1 is the virtual capacitance value of the system in steady state; α1 and α2 are the inertia coefficients;

[0027] (3) Absolute value of DC bus voltage change rate |dU dc When dt|≥δ, the system is in an unsteady state, indicating that the battery charge is either too high or too low, i.e., the State of Charge (SOC). min >SOC or SOC>SOC max To prevent battery overload, the energy storage port converter does not participate in operation. The DC bus system only adds inertia to the DC bus system through the main grid, treating the main grid as an equivalent virtual capacitor. At this time, the virtual capacitance value of the system is:

[0028] C3 = C2 + C bat

[0029] Among them, C bat Provides a virtual capacitance value for the energy storage port during unsteady-state conditions;

[0030] Among them, SOCmin State of Charge (SOC) is the minimum operating charge of the battery, while State of Charge (SOC) is the current charge of the battery. max Maximum working charge.

[0031] Furthermore, the different operating conditions in step 3 include:

[0032] Condition 1: The multi-port equipment detects that the system bus voltage change rate does not exceed the system set value. That is, the system bus voltage does not fluctuate, the system power is balanced, the input power of the photovoltaic and wind power ports is equal to the load output power, and the system is in a stable state. The converters of the energy storage port and the grid connection port do not participate in the system stability regulation.

[0033] Condition 2: The rate of change of the bus voltage of the multi-port equipment monitoring system is less than the system set value. That is, the system bus voltage drops, the system power is unbalanced, the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is in working charge. The battery and the grid participate in the bus voltage regulation. At this time, the converter at the energy storage port and the converter at the grid connection port switch to boost and rectification modes respectively to balance the bus voltage until the bus voltage stabilizes.

[0034] Operating Condition 3: The rate of change of the bus voltage of the multi-port equipment monitoring system is greater than the system set value. That is, the system bus voltage suddenly increases, the system power is unbalanced, the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is in working charge. The battery and the grid participate in the bus voltage regulation. At this time, the converter at the energy storage port and the converter at the grid connection port switch to buck and inverter modes respectively to balance the bus voltage until the bus voltage stabilizes.

[0035] Condition 4: The rate of change of the bus voltage of the multi-port equipment monitoring system is greater than the system set value. That is, the system bus voltage suddenly increases, the system power is unbalanced, the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is not at working charge, and only the grid participates in the bus voltage regulation. At this time, the grid-connected port converter switches to inverter mode to balance the bus voltage until the bus voltage stabilizes.

[0036] Condition 5: The rate of change of the bus voltage of the multi-port equipment monitoring system is greater than the system set value. At this time, the system bus voltage suddenly increases, the system power is unbalanced, the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is not in working charge, and only the grid participates in the bus voltage regulation. At this time, the grid-connected port converters switch to rectification mode to balance the bus voltage until the bus voltage stabilizes.

[0037] Beneficial effects:

[0038] This invention incorporates inertial coordination control into the grid-connected converter, leveraging the high inertia and high damping characteristics of the large power grid within the DC bus. This effectively maintains the power balance of the DC system. Furthermore, the large power grid's permanent energy exchange capability allows for continuous energy compensation to the DC system, playing a crucial role in maintaining DC bus voltage stability. In addition, this invention addresses battery overcharging / over-discharging issues by automatically disconnecting the energy storage port when the battery charge is too high or too low, thus preventing overload operation and extending battery life. This invention also possesses strong versatility; it remains applicable to similar multi-port intelligent power electronic devices. Attached Figure Description

[0039] Figure 1 This is a flowchart of the virtual inertial coordinated control method for multi-port intelligent power electronic devices of the present invention;

[0040] Figure 2 This is a diagram of the architecture of the multi-port intelligent power electronic device of the present invention;

[0041] Figure 3 This is a control block diagram of the virtual inertial coordination control method for multi-port intelligent power electronic devices of the present invention;

[0042] Figure 4 This is a block diagram of the energy storage port converter control of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0044] like Figure 1 As shown, the virtual inertial coordinated control method for multi-port intelligent power electronic devices of the present invention includes the following steps:

[0045] Step 1. Propose a control strategy for the DC bus system based on the control strategy for the AC bus system:

[0046] Based on the characteristics of large power grids, such as high damping, large inertia, and the ability to perform permanent energy exchange, a novel control system is established on the grid-connected port converter. By comparing the correspondence between DC and AC systems, the DC bus voltage U in the DC bus system is... dc The corresponding common bus angular frequency ω in the AC system, and the DC bus current I in the DC bus system. dcThe corresponding electromagnetic power output in the DC bus system corresponds to the parallel capacitor C in the DC bus system, which corresponds to the moment of inertia H in the AC bus system. Through analogy, the control equations of the synchronous generator in the AC bus system are transformed into virtual inertial control equations in the DC system.

[0047] The control equations for the synchronous generator in the AC bus system are:

[0048]

[0049] In the formula, ω n The rated angular frequency of the common bus; t is time, dω / dt is the rate of change of the angular frequency; P M P is the mechanical power input to the motor. E H is the electromagnetic power output by the motor; H is the damping coefficient; J is the virtual moment of inertia.

[0050] The virtual inertial control equations in the converted DC system are as follows:

[0051]

[0052] In the formula, i dc U is the current on the DC side of the power grid. dc_ref K is the reference value for the DC side voltage of the power grid. G U is the droop coefficient of the G-VSC droop control curve; dc C is the DC bus voltage; v This is the virtual capacitance value; dU dc / dt is the rate of change of the DC bus voltage.

[0053] Step 2. Determine the operating status of the port converter by measuring the bus voltage change rate:

[0054] Real-time monitoring of DC bus voltage change rate d Udc / dt and the battery charge SOC are expressed through the absolute value of the rate of change of the DC bus voltage |dU dc The value of / dt| is compared with the steady-state limit value δ set by the system, and it is determined whether the battery charge is at the working charge level. Based on the specific comparison, the value of the virtual capacitor required by the DC bus system is calculated, and the inertia of the DC system is provided by charging and discharging the virtual capacitor.

[0055] The virtual capacitance formula is discussed in three cases:

[0056] (1) Absolute value of DC bus voltage change rate |dU dc When dt| < δ, the system is in steady state. When the DC bus system is in steady state, the total system energy input power equals the load power used, i.e.:

[0057] Ppv +P wind =P Load

[0058] At this point, the system power is balanced, and neither the energy storage port converter nor the grid-connected port converter participates in operation. The virtual capacitance value required when the system DC bus voltage equals the set value is the initial set value of the steady-state system.

[0059] C v =C1

[0060] Where C1 is the virtual capacitance value of the system in steady state;

[0061] (2) Absolute value of DC bus voltage change rate |dU dc When |dt|≥δ, the system is in an unsteady state. If the battery charge is at its operating charge (SOC) at this point... min <SOC<SOC max At this time, the energy storage port converter and the grid connection port converter operate simultaneously.

[0062] When the multi-port device is in an unsteady state, the total system energy input power is not equal to the load power. If the battery charge is within the normal range, the grid-connected port converter and the energy storage port converter operate simultaneously. In this case, the main grid and the battery are equivalent to a virtual capacitor. Charging and discharging this virtual capacitor adds inertia to the system. The virtual capacitance value at this time is:

[0063]

[0064] In the formula, C1 is the virtual capacitance of the system in steady state; α1 and α2 are the inertia coefficients. SOC min State of Charge (SOC) is the minimum operating charge of the battery, while State of Charge (SOC) is the current charge of the battery. max Maximum working charge.

[0065] (3) Absolute value of DC bus voltage change rate |dU dc When dt|≥δ, the system is in an unsteady state, and the battery charge is either too high or too low (SOC). min >SOC or SOC>SOC max To prevent battery overload, the energy storage port converter does not participate in operation. The DC bus system only adds inertia to the DC bus system through the main grid, treating the main grid as an equivalent virtual capacitor. At this time, the virtual capacitance value of the system is:

[0066] C3 = C2 + C bat

[0067] Among them, C bat Provides a virtual capacitance value for the energy storage port during unsteady-state conditions;

[0068] Step 3. By observing the operating status of each port converter, the system operates under different conditions:

[0069] Condition 1: The multi-port equipment detects that the system bus voltage change rate does not exceed the system set value. At this time, the system bus voltage does not fluctuate, the system power is balanced, the input power of the photovoltaic and wind power ports equals the load output power, and the system is in a stable state. The converters at the energy storage port and the grid connection port do not participate in system stability regulation.

[0070] Condition 2: The rate of change of the bus voltage in the multi-port equipment monitoring system is less than the system set value. At this time, the system bus voltage drops, the system power is unbalanced, and the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is at its working charge level, and the battery and the grid participate in the bus voltage regulation. At this time, the converter at the energy storage port and the converter at the grid-connected port switch to boost and rectification modes respectively to balance the bus voltage until the bus voltage stabilizes.

[0071] Operating Condition 3: The rate of change of the bus voltage in the multi-port equipment monitoring system exceeds the system set value. At this time, the system bus voltage suddenly increases, the system power is unbalanced, and the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is at its working charge level, and the battery and the grid participate in the bus voltage regulation. At this time, the converter at the energy storage port and the converter at the grid-connected port switch to buck and inverter modes respectively to balance the bus voltage until the bus voltage stabilizes.

[0072] Condition 4: The rate of change of the bus voltage in the multi-port equipment monitoring system exceeds the system set value. At this time, the system bus voltage suddenly increases, the system power is unbalanced, and the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is not at working charge, and only the grid participates in the bus voltage regulation. At this time, the grid-connected port converter switches to inverter mode to balance the bus voltage until the bus voltage stabilizes.

[0073] Condition 5: The rate of change of the bus voltage in the multi-port equipment monitoring system exceeds the system set value. At this time, the system bus voltage suddenly increases, the system power is unbalanced, and the input power of both the photovoltaic and wind power ports is less than the load output power, placing the system in an unstable state. The equipment monitoring battery is not at its working charge level; only the grid participates in bus voltage regulation. In this situation, the converters at the grid-connected ports switch to rectification mode to balance the bus voltage until it stabilizes. Specific details are shown in Table 1.

[0074] Table 1

[0075]

[0076]

[0077] like Figure 2 As shown, the multi-port intelligent power electronic device of this invention includes six ports: photovoltaic (PV), wind power, battery, DC load, AC load, and power grid. Each port is connected to a DC bus via an inverter, which serves as the primary basis for measuring system power balance. The PV and wind power ports are connected to the DC bus using a boost circuit, while the battery is connected to the DC bus using a bidirectional DC / DC circuit. Excess energy is fed into the grid through a grid-connected converter. The DC load and AC load are connected to the DC bus via a boost converter and an inverter, respectively.

[0078] like Figure 3 As shown, the DC bus voltage U dc The rate of change of DC bus voltage, dU, is obtained after a differentiating step. dc / dt, real-time monitoring of DC bus voltage change rate dU dc / dt and the battery charge SOC are expressed through the absolute value of the rate of change of the DC bus voltage |dU dc The value of / dt| is compared with the steady-state limit δ set by the system, and it is determined whether the battery charge is at the working charge level. When the battery can work, the virtual capacitance value is... When the battery fails, the virtual capacitance value is C1 and C bat Provide virtual capacitance values ​​for steady-state virtual capacitance and battery respectively, and set C v With dU dc / dt、U dc The d-axis current reference value is obtained, and finally the grid-connected converter control signal is obtained through vector control and PWM generator.

[0079] Figure 4 The energy storage port converter control strategy of this invention, if U dc >U dc_ref If the voltage is above a certain level, it operates in Buck mode; otherwise, it operates in Boost mode. Secondly, the DC bus voltage U... dc DC bus voltage reference value U dc_ref The comparison is performed, and the comparison value is input into the PI control; it is determined whether the battery charge is at the working charge level. If not, the converter cannot work normally; if so, the converter works normally; finally, the comparison value between the battery current reference value and the battery current value is input into the PI control, and then the converter control signal is output.

[0080] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A virtual inertial coordinated control method for multi-port intelligent power electronic equipment, characterized in that, Includes the following steps: Step 1. Propose a control strategy for the DC bus system based on the control strategy for the AC bus system, including converting the control equations of the synchronous generator in the AC bus system into virtual inertial control equations in the DC system; The control equations for the synchronous generator in the AC bus system are: ； In the formula, ω n The rated angular frequency of the common bus; t is time, dω / dt is the rate of change of the angular frequency; P M P is the mechanical power input to the motor. E H is the electromagnetic power output of the motor; H is the damping coefficient; J is the virtual moment of inertia. The virtual inertial control equations in the converted DC system are as follows: ； In the formula, i dc U is the current on the DC side of the power grid. dc_ref The reference value for the DC side voltage of the power grid; KG is the droop coefficient of the G-VSC droop control curve; U dc C is the DC bus voltage. v This is the virtual capacitance value; dU dc / dt is the rate of change of the DC bus voltage; i dc_ref This is the reference value for the DC bus voltage; Step 2. When the DC bus voltage changes, the relevant port converters operate stably. The operating status of the port converters is determined by the rate of change of the DC bus voltage, including: firstly, real-time monitoring of the rate of change of the DC bus voltage dU. dc / dt and the battery charge SOC are expressed through the absolute value of the rate of change of the DC bus voltage |dU dc The value of / dt| is compared with the steady-state limit value δ set by the system, and it is determined whether the battery charge is at the working charge level. Based on the specific comparison, the value of the virtual capacitor required by the DC bus system is calculated, and the inertia of the DC system is provided by charging and discharging the virtual capacitor. The formula for the virtual capacitance includes: (1) Absolute value of DC bus voltage change rate |dU dc When dt| < δ, the system is in steady state. When the DC bus system is in steady state, the total system energy input power equals the load power used, i.e.: ； At this point, the system power is balanced, and neither the energy storage port converter nor the grid-connected port converter participates in operation. The virtual capacitance value required when the system DC bus voltage equals the set value is the steady-state system virtual capacitance value: ； Where C1 is the virtual capacitance value of the system in steady state; (2) Absolute value of DC bus voltage change rate ≥δ, at which point the system is in an unsteady state; if the battery charge is at its working charge, i.e., SOC. min <SOC<SOC max At this time, the energy storage port converter and the grid-connected port converter operate simultaneously. When the multi-port equipment is in an unsteady state, the total system energy input power is not equal to the load power. If the battery charge is within the normal charge range, and the grid-connected port converter and the energy storage port converter operate simultaneously, the main grid and the battery are equivalent to a virtual capacitor. The inertia of the system is increased by charging and discharging the virtual capacitor. At this time, the value of the virtual capacitor is: ； In the formula, C1 is the virtual capacitance value of the system in steady state; α1 and α2 are the inertia coefficients; (3) Absolute value of DC bus voltage change rate |dU dc When dt|≥δ, the system is in an unsteady state, indicating that the battery charge is either too high or too low, i.e., the State of Charge (SOC). min >SOC or SOC>SOC max To prevent battery overload, the energy storage port converter does not participate in operation. The DC bus system only adds inertia to the DC bus system through the main grid, treating the main grid as a virtual capacitor. At this time, the virtual capacitance value of the system is: ； Among them, C bat Provides a virtual capacitance value for the energy storage port during unsteady-state conditions; Among them, SOC min The minimum operating charge of the battery, SOC (State of Charge), is the current charge of the battery. max Maximum working charge; Step 3. The system operates under different conditions based on the working status of each port converter.

2. The virtual inertial coordinated control method for a multi-port intelligent power electronic device according to claim 1, characterized in that, The different operating conditions in step 3 include: Condition 1: The multi-port equipment detects that the system bus voltage change rate does not exceed the system set value. At this time, the system bus voltage does not fluctuate, the system power is balanced, the input power of the photovoltaic and wind power ports is equal to the load output power, and the system is in a stable state; the converters of the energy storage port and the grid connection port do not participate in the system stability regulation. Condition 2: The bus voltage change rate of the multi-port equipment monitoring system is less than the system set value. At this time, the system bus voltage drops, the system power is unbalanced, the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is in working charge. The battery and the grid participate in the bus voltage regulation. At this time, the energy storage port converter and the grid-connected port converter switch to boost and rectification modes respectively to balance the bus voltage until the bus voltage stabilizes. Condition 3: The rate of change of the bus voltage of the multi-port equipment monitoring system is greater than the system set value. At this time, the system bus voltage suddenly increases, the system power is unbalanced, the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is in working charge. The battery and the grid participate in the bus voltage regulation. At this time, the converter at the energy storage port and the converter at the grid connection port switch to buck and inverter modes respectively to balance the bus voltage until the bus voltage stabilizes. Condition 4: The rate of change of the bus voltage of the multi-port equipment monitoring system is greater than the system set value. At this time, the system bus voltage suddenly increases, the system power is unbalanced, and the input power of the photovoltaic and wind power ports is less than the load output power. At this time, the system is in an unstable state. The equipment monitoring battery is not at working charge. Only the grid participates in the bus voltage regulation. At this time, the grid-connected port converter switches to inverter mode to balance the bus voltage until the bus voltage stabilizes. Condition 5: The rate of change of the bus voltage of the multi-port equipment monitoring system is greater than the system set value. At this time, the system bus voltage suddenly increases, the system power is unbalanced, the input power of the photovoltaic and wind power ports is less than the load output power, and the system is in an unstable state. The equipment monitoring battery is not in working charge, and only the grid participates in the bus voltage regulation. At this time, the grid-connected port converters switch to rectification mode to balance the bus voltage until the bus voltage stabilizes.

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