Control system and method for full-condition multi-inverter parallel driving MGP

Abstract

This invention relates to a control system for parallel driving of multiple inverters (MGP) under all operating conditions. The system comprises a signal acquisition and processing unit, an inverter current loop control unit, a pulse modulation unit, an energy processing unit, and a synchronous motor pair connected in sequence. The energy processing unit is connected to the renewable energy power station, and the synchronous motor pair is connected to the power grid. The control system also includes a unity power factor control unit connected to the signal acquisition and processing unit, with its output connected to the inverter current loop control unit. Based on the ratio of inverter current to rated inverter capacity and the ratio of the rated capacity of the MGP to the rated capacity of the renewable energy power station, this invention constructs an inverter current distribution coefficient. By automatically and dynamically adjusting the inverter current distribution coefficient, the system effectively adapts to various operating conditions, such as equal capacity and output, and unequal capacity and output, when multiple inverters from a renewable energy power station drive the MGP in parallel, thus better matching the power transmission between each inverter and the MGP.

Description

Technical Field

[0001] This invention belongs to the field of power generation grid connection control, specifically relating to a control system for multi-inverter parallel drive MGP under all operating conditions. Background Technology

[0002] With the gradual replacement of thermal power units by large-scale renewable energy sources, the power grid will exhibit characteristics such as low inertia and high power electronics, which are detrimental to the stable operation of the grid. The use of Motor-Generator Pair (MGP) technology for intermittent renewable energy grid connection has been a research direction in recent years. This technology can endow renewable energy power plants with the excellent properties of synchronous motors, which is beneficial to the stable operation of the power grid. The excellent properties of renewable energy power plants acquired by MGP technology mainly include: 1) the renewable energy power plant possesses real rotational inertia, strong inertial response, and increased frequency support capability of the power grid; 2) during grid faults, it can provide damping and reactive power support, accelerating grid voltage recovery; 3) it improves the high and low voltage ride-through capability of renewable energy power plants.

[0003] Due to the high difficulty and poor economic efficiency of designing a single large-capacity inverter, using multiple inverters in parallel to drive a multi-inverter power generation system (MGP) is an inevitable choice to meet the capacity requirements of renewable energy power plants. Current research on multi-inverter parallel-driven MGPs is limited, and mainly focuses on parallel connections of multiple inverters with equal capacity and output. Existing vector i for multi-inverter parallel-driven MGPs... d =0 control strategy has certain limitations. When the MGP output is high, the output power factor of the inverter connected to the MGP input side may be too low, making it difficult to guarantee the active power transmission of the MGP. In practice, renewable energy power plants are intermittent and random, making it impossible to guarantee that the output of renewable energy and MGP will always be at a low level. In other words, existing methods are difficult to meet the active power transmission requirements of renewable energy power plants.

[0004] Therefore, this study investigates a control method that can guarantee the active power output of the MGP under all operating conditions of the new energy power station, regardless of the magnitude of the output of the new energy source and the MGP. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a control system for parallel driving of multiple inverters for MGP under all operating conditions. This system can ensure the active power output of MGP under all operating conditions of the renewable energy plant, regardless of the output of renewable energy and MGP. This makes the impact of renewable energy and MGP on the power factor of the inverter output side close to zero, and the power factor of the inverter output side close to the unity power factor (UPF).

[0006] The technical solution of this invention is a control system for multi-inverter parallel drive MGP under all operating conditions, including a signal acquisition and processing unit, an inverter current loop control unit, a pulse modulation unit, an energy processing unit, and a synchronous motor pair connected in sequence; the energy processing unit is connected to the new energy power station, and the synchronous motor pair is connected to the power grid.

[0007] The signal acquisition and processing unit acquires the rotor angle ω of the synchronous motor pair. t The stator d-axis and q-axis currents i of a synchronous motor sd i sq Collect the three-phase current i on the output side of each inverter. abc And according to the rotor angle ω t Transform it into the corresponding value in the dq coordinate system; collect the three-phase voltage e at the inverter parallel connection point. abc And according to the rotor angle ω t Convert the values ​​to their corresponding values ​​in the dq coordinate system; collect the current reference values ​​of each inverter; and obtain the reference values ​​of the stator current of the synchronous motor in the synchronous motor pair based on the capacity relationship between the synchronous motor pair and the inverter.

[0008] The inverter current loop control unit performs decoupling control of the two-phase synchronous rotating coordinate system based on the inverter output voltage and current in the dq coordinate system obtained by the signal acquisition and processing unit, thereby obtaining the voltage reference value in the dq axis coordinate and realizing the decoupling control of the grid-connected inverter output power.

[0009] The pulse modulation unit controls the voltage reference value v of the output of each inverter current loop. i，d v i，q The voltage is converted into the corresponding three-phase voltage, and the trigger signal of each inverter is obtained by sinusoidal pulse width modulation, thereby realizing the parallel driving of synchronous motor pairs by multiple inverters.

[0010] The energy processing unit includes multiple sets of three-phase inverters and LC filters.

[0011] Synchronous motor pairs include a synchronous motor and a synchronous generator connected coaxially. The synchronous motor converts electrical energy in the new energy power station into mechanical energy, while the synchronous generator, driven by the synchronous motor, converts the mechanical energy back into electrical energy.

[0012] Preferably, the control system further includes a unity power factor control unit connected to the signal acquisition and processing unit, and the output of the unity power factor control unit is connected to the inverter current loop control unit. The unity power factor control unit uses the unity factor method to calculate the stator d-axis and q-axis currents of the synchronous motor, so that the power factor of the synchronous motor pair is close to or equal to 1.

[0013] Furthermore, the inverter current loop control unit performs decoupling control of the two-phase synchronous rotating coordinate system through the inverter current loop, thereby obtaining the voltage reference value in the dq axis coordinate system; the inverter current loop control is established according to the loop control equation of the inverter output side in the form of the dq coordinate system, and the voltage and current output by the inverter are transformed into voltage and current in the dq coordinate system through the rotor angle ωt of the synchronous motor.

[0014] The control method of the control system of the multi-inverter parallel drive MGP under all operating conditions directly collects the stator d and q axis currents of the synchronous motor to calculate the flux linkage ψ, and uses the flux linkage ψ as a known quantity to calculate the reference currents of the stator d and q axes of the synchronous motor.

[0015] Preferably, the control method is applicable to all operating conditions where multiple inverters are connected in parallel, and each inverter has equal or unequal capacity and the same or different output. The current is allocated according to the output of each inverter, and the current allocation coefficient is as follows:

[0016]

[0017] In the formula k i Let i be the current distribution coefficient for the i-th inverter; i is the current reference value of the i-th inverter, obtained as a per-unit value based on the rated capacity of the i-th inverter; m is the ratio of the synchronous motor pair to the rated capacity of the new energy power station; the ratio of the rated capacities of multiple inverters is n1:n2:n3:...:n N n i , i = 1, 2, 3...N represents the rated capacity of the i-th inverter, where N represents the number of inverters.

[0018] Compared with the prior art, the beneficial effects of the present invention include:

[0019] 1) The control system for multi-inverter parallel drive MGP under all operating conditions of the present invention constructs an inverter current distribution coefficient based on the ratio of inverter current, inverter rated capacity, and MGP to rated capacity of new energy power station. By automatically and dynamically adjusting the inverter current distribution coefficient, the system can adapt well to various operating conditions such as equal capacity and output, and unequal capacity and unequal output when multiple inverters drive MGP in parallel at new energy power station, and better match the power transmission between each inverter and MGP.

[0020] 2) The control system of the multi-inverter parallel drive MGP of the present invention makes the power factor of the inverter output side close to 1, effectively ensuring the active power transmission efficiency of new energy through the grid connection of MGP; regardless of the output status of new energy and MGP, the influence of new energy and MGP on the power factor of inverter output side is almost zero.

[0021] 3) The control method of the present invention adopts a vector UPF control strategy. By collecting the stator d and q axis reference currents of the synchronous motor in the MGP, the flux linkage is calculated. By utilizing the negative feedback characteristics of the flux linkage and the stator d axis current of the synchronous motor, the calculation process can be reduced from solving a multivariate cubic equation to a direct solution, which greatly simplifies the calculation.

[0022] 4) The control system and corresponding control method of the multi-inverter parallel drive MGP of the present invention are more in line with engineering practice and can be widely promoted and used. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a schematic diagram of the control system for a multi-inverter parallel drive MGP under all operating conditions, according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of a synchronous motor pair according to an embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram of the energy processing unit according to an embodiment of the present invention.

[0027] Figure 4 This is a schematic diagram of the inverter current loop control principle according to an embodiment of the present invention.

[0028] Figure 5 This is a schematic diagram of vector unity power factor control for a multi-inverter parallel-driven MGP according to an embodiment of the present invention.

[0029] Figure 6 This is a schematic diagram of three inverters connected in parallel to drive an MGP.

[0030] Figure 7 This is a graph showing the power factor on the inverter output side under the vector UPF control mode according to an embodiment of the present invention.

[0031] Figure 8 This is a graph showing the active power output of three inverters under the condition of equal capacity.

[0032] Figure 9 The graph shows the active power output curves of the MGP and the inverter under the same capacity conditions.

[0033] Figure 10 The graph shows the active power output curves of three inverters under non-equal capacity conditions.

[0034] Figure 11 The graph shows the active power output curves of the MGP and the inverter under non-equal capacity conditions. Detailed Implementation

[0035] like Figure 1 As shown, the control system for multi-inverter parallel drive MGP under all operating conditions includes a signal acquisition and processing unit, an inverter current loop control unit, a pulse modulation unit, an energy processing unit, and a synchronous motor pair connected in sequence; the energy processing unit is connected to the new energy power station, and the synchronous motor pair is connected to the power grid.

[0036] In this embodiment, the control system for the multi-inverter parallel drive MGP under all operating conditions also includes a unity power factor control unit connected to the signal acquisition and processing unit. The output of the unity power factor control unit is connected to the inverter current loop control unit. The unity power factor control unit uses the unity factor method to calculate the stator d-axis and q-axis currents of the synchronous motor, so that the power factor of the synchronous motor of the synchronous motor pair is close to or equal to 1.

[0037] like Figure 2 As shown, a synchronous motor pair consists of a synchronous motor and a synchronous generator connected coaxially. The synchronous motor converts the electrical energy of the new energy power station into mechanical energy, while the synchronous generator, driven by the synchronous motor, converts the mechanical energy back into electrical energy.

[0038] The energy processing unit includes multiple sets of three-phase inverters and LC filters, one of which has the following structure: Figure 3 As shown.

[0039] The signal acquisition and processing unit acquires the rotor angle ωt and the stator d-axis and q-axis currents i of the synchronous motor in the MGP system. sd i sq Collect the three-phase current i on the output side of each inverter. abc The rotor angle ωt is used to transform the voltage into a dq coordinate system; the three-phase voltage e at the inverter parallel connection is collected. abc The rotor angle ωt is used to transform the current into the dq coordinate system; the current reference values ​​of each inverter are collected, and the reference values ​​of the synchronous motor stator current in the MGP are obtained through the capacity relationship between the MGP and the inverter.

[0040] The inverter current loop control unit performs decoupling control of the two-phase synchronous rotating coordinate system based on the inverter output voltage and current in the dq coordinate system obtained by the signal acquisition and processing unit, thereby obtaining the voltage reference value in the dq axis coordinate and realizing the decoupling control of the grid-connected inverter output power.

[0041] Pulse modulation unit: controls the voltage reference value v output by each inverter current loop. i,d v i，q The voltage is converted into the corresponding three-phase voltage, and the trigger signal of each inverter is obtained through SPWM, thereby realizing the parallel drive of MGP by multiple inverters.

[0042] To achieve power decoupling, the grid-connected control of inverters typically adopts the dq coordinate system form, and its output-side loop control equations are as follows:

[0043]

[0044] In the formula: u d u q i represents the d-axis and q-axis components of the inverter output voltage; d i q e represents the d-axis and q-axis components of the inverter output current; d e q These are the d-axis and q-axis components of the grid-connected voltage.

[0045] Establish according to formula (1) Figure 4 The inverter current loop control shown converts the inverter output voltage and current into voltage and current in the dq coordinate system through the rotor angle ωt in the MGP. Decoupling control of the two-phase synchronous rotating coordinate system is achieved through the inverter current loop, thereby obtaining the voltage reference value in the dq axis coordinate system, and thus realizing decoupling control of the grid-connected inverter output power.

[0046] The voltage, current and other parameters in the inverter current loop control are all per-unit values, and the parameters in other controls below are also per-unit values.

[0047] The torque expression for a synchronous motor in the dq coordinate system is:

[0048] T e =1.5n p (ψ sd i sq -ψ sq i sd (2)

[0049] Where: n p ψ is the number of pole pairs of the synchronous motor; sd ψ sq i represents the d-axis and q-axis components of the stator flux linkage of a synchronous motor. sd i sq These are the d-axis and q-axis components of the stator current of the synchronous motor.

[0050] Combining inverter current loop control and equation (2), it can be seen that when multiple inverters drive the MGP in parallel, the magnitude of the stator d-axis and q-axis currents of the motor can be changed by inverter current loop control, thereby adjusting the electromagnetic torque of the motor and achieving the purpose of controlling the power transmission of the MGP. Therefore, the calculation of the stator d-axis and q-axis currents of the synchronous motor is of paramount importance.

[0051] To ensure the full utilization of electrical energy in renewable energy power plants, the active power output of the synchronous motor (MGP) should be controlled to maximize its potential. This means ensuring the power factor of the synchronous motor within the MGP is as close to 1 as possible. Therefore, the unit factor method can be used to calculate the stator d-axis and q-axis currents of the synchronous motor. The specific calculation process is as follows:

[0052] The stator of a synchronous motor is typically used with the input current as the positive current direction. In this case, its d-axis and q-axis voltage and flux linkage equations are:

[0053]

[0054]

[0055] In the formula, u sd u sq i represents the d-axis and q-axis components of the stator voltage of the synchronous motor. f i is the excitation current; Dd i Dq R represents the d-axis and q-axis components of the current in the damping winding. s L is the stator equivalent resistance; d L q L represents the d-axis and q-axis equivalent inductance of the stator winding. md L mq The armature inductance is induced along the d and q axes.

[0056] When a synchronous motor is operating in steady state, its stator voltage, current, and flux linkage are all constant values ​​that do not change with time, and there is no induced current in the rotor damping winding. Therefore, the differential component of the flux linkage is 0. Dd =i Dq =0. If the effect of stator resistance is ignored, equation (3) can be simplified to:

[0057]

[0058] In the formula, ψ=L md i f , which is the magnetic flux generated by the excitation current on the armature induced inductance of the d-axis.

[0059] However, considering that in the synchronous motor simulation model in MATLAB / Simulink, the stator uses the output current as the positive direction, when solving for the stator d-axis and q-axis currents using the unity power factor method, the synchronous motor stator uses the output current as the positive direction. In this case, the voltage and flux linkage equations of the synchronous motor are as follows:

[0060]

[0061]

[0062] Combining equations (2) and (7), the torque expression of the synchronous motor in the dq coordinate system can be written as:

[0063] T e =15n p [ψi sq -(L d -L q )i sd i sq (8)

[0064] Since the per-unit expression for the torque of a synchronous motor does not include 1.5n. p Therefore, the per-unit expression for the magnetic flux linkage ψ is:

[0065]

[0066] When a synchronous motor meets the unity power factor condition, its stator voltage and current are in phase, that is:

[0067]

[0068] Combination Equation (10) can be transformed to obtain:

[0069]

[0070] According to equation (10), solutions exceeding the maximum current value are removed, i sd You can use i s express:

[0071]

[0072] Synchronous motor stator q-axis current i sq It can be represented as:

[0073]

[0074] The core of vector UPF control of synchronous motor is to calculate the reference values ​​of the stator d and q axis currents of synchronous motor through equations (9), (12), and (13), so as to ensure that the power factor of synchronous motor is close to or equal to 1.

[0075] Solving multivariate cubic equations is quite complex, but if the flux linkage ψ can be calculated directly from the stator d-axis and q-axis currents of a synchronous motor, and the flux linkage ψ can be treated as a known quantity, then the reference currents of the stator d-axis and q-axis of the synchronous motor can be calculated directly, which will greatly reduce the calculation difficulty.

[0076] Assuming that the stator d-axis and q-axis currents of the synchronous motor can be directly collected to calculate the flux linkage ψ, it can be seen from equations (9) and (13) that the flux linkage ψ is related to the direct collection of the stator d-axis current i sdThe derivative is:

[0077]

[0078] In the formula: the electromagnetic torque T of the synchronous motor stator is defined by taking the output current as the positive direction of the current. e When the value is negative and the stator d-axis current i is controlled by unity power factor, sd When positive, the stator q-axis current i sq It is a negative value.

[0079] From (12) and (13), it can be seen that the reference current is... The derivative of the magnetic flux linkage ψ is:

[0080]

[0081] From equations (14) and (15), it can be seen that when the magnetic flux ψ is less than its actual value, the calculated current... This will result in the stator d-axis current i being greater than its actual value, thus causing the synchronous motor output to... sd Increase, while i sd An increase in flux linkage ψ will lead to an increase in flux linkage ψ, which in turn will affect the calculation of current. Decrease, and finally the magnetic flux ψ, i sd The flux linkage ψ will approach its actual value. Therefore, when directly collecting the stator d-axis and q-axis currents of the synchronous motor to calculate the flux linkage ψ, the flux linkage ψ and the stator d-axis current of the synchronous motor have negative feedback characteristics. Therefore, using this method to simplify the calculation is a feasible solution.

[0082] k i Let k be the current distribution coefficient for the i-th inverter. Since the stator current of the synchronous motor is in the positive direction at the output, which is opposite to the direction of the inverter output current, k... i It is a negative value.

[0083] When multiple inverters of equal capacity and output are connected in parallel, and the rated capacity of the MGP is the same as that of the new energy power station, its current distribution coefficient k i for:

[0084] k i =-1 (16)

[0085] However, parallel connection of multiple inverters with equal capacity and output is only applicable to a single photovoltaic power station or wind farm, and the light intensity or wind speed in the new energy power station must be the same by default.

[0086] To ensure that parallel operation of multiple inverters is applicable to all operating conditions where each inverter has equal or unequal capacity and the same or different output, this paper allocates current according to the output of each inverter, with the current allocation coefficient being:

[0087]

[0088] In the formula: i i This is the current reference value of the i-th inverter, obtained as a per-unit value based on the rated capacity of the i-th inverter; the ratio of the rated capacities of multiple inverters is n1:n2:n3:......:n N m is the ratio of MGP to the rated capacity of the new energy power station.

[0089] At this time, multiple inverters connected in parallel are not only suitable for single photovoltaic power stations or wind farms, but also for new energy power stations that contain both wind and photovoltaic power; not only suitable for new energy power stations with identical environmental factors such as light intensity and wind speed, but also suitable for new energy power stations with different environmental factors such as light intensity and wind speed; not only suitable for centralized new energy power station drives, but also suitable for distributed new energy power stations.

[0090] Based on the above analysis, and combining inverter current loop control with synchronous motor vector UPF control, we can obtain the following: Figure 5 The diagram shows a vector UPF control structure for a multi-inverter parallel drive MGP. In the diagram, the inverter model is YLSSL, the synchronous motor model is TZH-200S4-TH, the filter model is SLFL15-1R710G-01TF, and the parameters in the control strategy are per-unit values.

[0091] Figure 6 This is a schematic diagram of a three-inverter parallel drive MGP. During the simulation, the total rated capacity of the new energy power station is set to 60MVA, the rated capacity of the two inverters is the same, the DC power supply voltage is set to 500V, and the rated voltage of the synchronous motor in the MGP is 4000V.

[0092] Example 1: Vector UPF Control of MGP

[0093] This study investigates the parallel driving of a multi-inverter MGP under vector UPF control mode. The rated capacity of the MGP is set to be equal to the rated capacity of the new energy source, and the output of the two inverters is kept the same. The different outputs of the new energy source are simulated by setting the reference values ​​of the inverter current to 1, 0.9, 0.8, ..., 0.2, 0.1. The simulation results are shown in Table 1.

[0094] As shown in Table 1, although the power factor on the inverter output side still shows a decreasing trend when the output of new energy sources and MGP increases under vector UPF control mode, the decreasing trend is extremely insignificant. When the output of new energy sources is 10%, the power factor on the inverter output side can reach 0.99998, while when the output of new energy sources is at its rated level, the power factor on the inverter output side can reach 0.99838, with a difference of only 0.0016. It can be seen that the change in the output of new energy sources and MGP has almost zero impact on the power factor on the inverter output side.

[0095] Table 1 Power Factor Table of Inverter Output Side under UPF Mode

[0096]

[0097] The ratio of MGP to the rated capacity of the renewable energy power station was set to m. The above simulations were performed with m taking values ​​of 1, 2, 4, and 6. The simulation results are shown in [the table below]. Figure 7 .

[0098] Depend on Figure 7 It can be seen that when m is 1, 2, 4, and 6, the inverter output-side power factor reaches its minimum value under the rated output of the renewable energy source, which is 0.99838, 0.99959, 0.99990, and 0.99996 respectively. Therefore, although under the same renewable energy output, the larger m is, the lower the MGP output and the smaller the inverter output-side power factor, the change in the inverter output-side power factor is negligible. Thus, when the rated capacity of the MGP equals the rated capacity of the renewable energy source, the inverter output-side power factor can reach above 0.998, which is sufficient to ensure the active power transmission efficiency of renewable energy source grid connection via the MGP.

[0099] In vector UPF control mode, the power factor of the parallel output of multiple inverters connected to the MGP output side can only reach 0.998, which is close to 1. The main reason why it is difficult to reach 1 is that the influence of the dynamic changes of the equivalent resistance and current parameters of the synchronous motor stator is ignored in the calculation of the synchronous motor stator current. In the inverter current loop control, the current of the filter capacitor branch is ignored, and the inverter output current is assumed to be the current flowing into the synchronous motor stator.

[0100] Example 2: Full-condition study of vector UPF control mode

[0101] 1) Parallel drive of multiple inverters of equal capacity to MGP

[0102] Set the current reference values ​​for the three inverters to i1, i2, and i3, and the current reference value for the MGP to i. s The rated capacity ratio of the three inverters, n1:n2:n3, is 1:1:1. At the initial simulation time, i1, i2, and i3 are all set to 1. At 10s, i1, i2, and i3 are all reduced to 0.8 to simulate equal capacity and same output. At 15s, i1 is reduced to 0.6, i2 is reduced to 0.7, and i3 remains unchanged to simulate equal capacity but different output. Simulation results are shown below. Figure 8 , Figure 9 And Table 2, where P1, P2, and P3 are the active power outputs of inverters 1, 2, and 3, respectively; P 123 P represents the total active power output of the three inverters. MGP The MGP outputs active power.

[0103] Depend on Figure 8 It can be seen that, under the same capacity, when the inverter current command changes in the same way at 10 seconds, the output of the three inverters is the same, and they can quickly respond to the change in current command; when the inverter command changes in different ways at 15 seconds, the output of the three inverters is different, and they follow their own current command changes respectively.

[0104] Depend on Figure 9 It can be seen that, under the same capacity, regardless of whether the output is the same or different, the active power output of the MGP always follows the total active power output of the inverter. Moreover, when the output of the new energy power station changes, the transient process of the inverter does not exceed 0.5s, and the transient process of the MGP does not exceed 3s.

[0105] As shown in Table 2, under the same capacity, whether the output power is the same or different, the active power output of each inverter and MGP is basically proportional to its own current command.

[0106] Table 2. Active power output of inverter and MGP under equal capacity.

[0107]

[0108] 2) Parallel drive of multiple inverters with unequal capacity for MGP

[0109] The rated capacity ratio of the three inverters, n1:n2:n3, is set to 3:2:1. At the initial simulation time, i1, i2, and i3 are all set to 1. At 10s, i1, i2, and i3 are all reduced to 0.8 to simulate equal capacity and same output. At 15s, i1 is reduced to 0.6, i2 is reduced to 0.7, and i3 remains unchanged to simulate equal capacity but different output. Simulation results are shown below. Figure 10 , Figure 11 And Table 3.

[0110] Depend on Figure 10 It can be seen that, under unequal capacity conditions, regardless of whether the output is the same or different, the output of the three inverters follows the changes in their respective current commands.

[0111] Depend on Figure 11 It can be seen that, under non-equal capacity conditions, regardless of whether the output power is the same or different, the active power output of the MGP always follows the total active power output of the inverter.

[0112] As shown in Table 3, under the same capacity, whether the output power is the same or different, the active power output of each inverter and MGP is basically proportional to its own current command.

[0113] Table 3 Active Power Output of Non-Uniform Capacity Inverters and MGP

[0114]

[0115] In the vector UPF control of a multi-inverter parallel-driven MGP, the existence of the current distribution coefficient ki ensures that the power output of each inverter and the MGP can be well guaranteed, even when the capacity of the multiple inverters is equal or unequal, or their output is the same or different.

Claims

1. A control system for multi-inverter parallel drive MGP under all operating conditions, characterized in that, It includes a signal acquisition and processing unit, an inverter current loop control unit, a pulse modulation unit, an energy processing unit, and a synchronous motor pair connected in sequence; the energy processing unit is connected to the new energy power station, and the synchronous motor pair is connected to the power grid; The signal acquisition and processing unit acquires the rotor angle of the synchronous motor pair. The stator d-axis and q-axis currents of a synchronous motor i sd , i sq Collect the three-phase current on the output side of each inverter. i abc And according to the rotor angle Transform it into the corresponding value in the dq coordinate system; collect the three-phase voltage at the inverter parallel connection point. e abc And according to the rotor angle Transform it into the corresponding value in the dq coordinate system; collect the current reference value of each inverter, and obtain the reference value of the stator current of the synchronous motor in the synchronous motor pair according to the capacity relationship between the synchronous motor pair and the inverter; The inverter current loop control unit performs decoupling control of the two-phase synchronous rotating coordinate system based on the inverter output voltage and current in the dq coordinate system obtained by the signal acquisition and processing unit, thereby obtaining the voltage reference value in the dq coordinate system and realizing the decoupling control of the grid-connected inverter output power. The pulse modulation unit controls the voltage reference value output by each inverter current loop. v i,d , v i,q The voltage is converted into the corresponding three-phase voltage, and the trigger signal of each inverter is obtained by sinusoidal pulse width modulation, thereby realizing the parallel drive of synchronous motor pairs by multiple inverters; The energy processing unit includes multiple sets of three-phase inverters and LC filters; Synchronous motor pairs include a synchronous motor and a synchronous generator connected coaxially. The synchronous motor converts electrical energy in the new energy power station into mechanical energy, while the synchronous generator, driven by the synchronous motor, converts the mechanical energy back into electrical energy.

2. The control system for multi-inverter parallel drive MGP under all operating conditions according to claim 1, characterized in that, The control system also includes a unity power factor control unit connected to the signal acquisition and processing unit, and the output of the unity power factor control unit is connected to the inverter current loop control unit. The unity power factor control unit uses the unity factor method to calculate the stator d-axis and q-axis currents of the synchronous motor, so that the power factor of the synchronous motor is close to or equal to 1.

3. The control system for multi-inverter parallel drive MGP under all operating conditions according to claim 2, characterized in that, The inverter current loop control unit performs decoupling control of the two-phase synchronous rotating coordinate system through the inverter current loop, thereby obtaining the voltage reference value in the dq axis coordinate. To achieve power decoupling, the grid-connected control of inverters typically adopts the dq coordinate system form, and the loop control equations on the inverter output side are as follows: ； (1) In the formula These represent the d-axis and q-axis components of the inverter output voltage, respectively. These represent the d-axis and q-axis components of the inverter output current, respectively. These represent the d-axis and q-axis components of the grid-connected voltage, respectively. The inverter current loop control is established according to equation (1), and the rotor angle of the synchronous motor is controlled by the equation (1). This converts the voltage and current output by the inverter into voltage and current in the dq coordinate system.

4. The control system for multi-inverter parallel drive MGP under all operating conditions according to claim 3, characterized in that, The unit factor method is used to calculate the stator d-axis and q-axis currents of the synchronous motor. Torque of a synchronous motor in the dq coordinate system The expression is as follows: ； (2) In the formula: This represents the number of pole pairs of the synchronous motor. These represent the d-axis and q-axis components of the stator flux linkage of the synchronous motor, respectively. These represent the d-axis and q-axis components of the stator current of the synchronous motor, respectively. Combining inverter current loop control and equation (2), it can be seen that when multiple inverters drive synchronous motor pairs in parallel, the magnitude of the stator d and q axis currents of the motor can be changed by inverter current loop control, thereby achieving the adjustment of the electromagnetic torque of the motor and the purpose of controlling the power transmission of the synchronous motor. If the stator input current of the synchronous motor is taken as the positive direction of the current, then its d-axis voltage and q-axis flux linkage equations are: ；(3) ； (4) In the formula These represent the d-axis and q-axis components of the stator voltage of the synchronous motor, respectively. It is the excitation current; These represent the d-axis and q-axis components of the current in the damping winding, respectively. The stator equivalent resistance; These represent the d-axis and q-axis equivalent inductances of the stator windings, respectively. These represent the armature inductance along the d and q axes, respectively. When a synchronous motor is operating in steady state, its stator voltage, current, and flux linkage are all constant values ​​that do not change with time, and there is no induced current in the rotor damping winding. Therefore, the differential component of the flux linkage is 0. i Dd = i Dq =0; If the effect of stator resistance is neglected, equation (3) can be simplified to: ； (5) In the formula, The magnetic flux generated by the excitation current on the armature induced inductance of the d-axis; ； Considering that in the synchronous motor simulation model, the stator uses the output current as the positive direction, when solving for the stator d-axis and q-axis currents using the unity power factor method, the synchronous motor stator uses the output current as the positive direction. In this case, the voltage and flux linkage equations of the synchronous motor are as follows: ；(6) ；(7) Combining equations (2) and (7), the torque expression of the synchronous motor in the dq coordinate system is as follows: ； (8) Since the per-unit expression for synchronous motor torque does not include 1.

5. n p Item, therefore magnetic linkage ψ The per-unit expression is: ；(9) When a synchronous motor meets the unity power factor condition, its stator voltage and current are in phase, that is: ； (10) Combination By transforming equation (10), we obtain: ； (11) According to equation (11), solutions exceeding the maximum current value are removed. i sd Available i s It is expressed as follows: ； (12) Synchronous motor stator q-axis current i sq It can be represented as: ； (13) The core of vector unit power factor control of synchronous motor is to calculate the reference values ​​of the stator d and q axis currents of synchronous motor through equations (9), (12), and (13), so as to ensure that the power factor of synchronous motor is close to or equal to 1.

5. The control method for the control system of multi-inverter parallel drive MGP under all operating conditions as described in claim 4, characterized in that, The control method directly collects the stator d-axis and q-axis currents of the synchronous motor to calculate the flux linkage. ψ , magnetic chain ψ Treating these as known quantities, the reference currents of the d and q axes of the synchronous motor stator can be calculated. From equations (8) and (12), it can be seen that the magnetic flux ψ Direct acquisition of stator d-axis current i sd The derivative is: ； (14) In the formula: the electromagnetic torque of the synchronous motor stator is defined by taking the output current as the positive direction of the current. T e When the value is negative and the stator d-axis current is under unity power factor control, i sd The stator q-axis current is positive. i sq It is a negative value; From (12) and (13), it can be seen that the reference current is... magnetic flux ψ The derivative is: ； (15) From equations (14) and (15), it can be seen that when the magnetic flux... ψ When the current is less than its actual value, calculate the current. This will result in a stator d-axis current output by the synchronous motor that is greater than its actual value. i sd Increase, and i sd The increase in flux will lead to magnetic flux ψ Increase, magnetic flux ψ The increase in [the value] will further affect its calculation of current. Reduce, final magnetic flux ψ , i sd It will approach its actual value; Therefore, the flux linkage should be calculated by directly collecting the stator d-axis and q-axis currents of the synchronous motor. ψ At that time, magnetic chain ψ Since the stator d-axis current of a synchronous motor has negative feedback characteristics, it is feasible to use this method to simplify the calculation.

6. The control method according to claim 5, characterized in that, The method described above is applicable to all operating conditions where multiple inverters can be connected in parallel, with each inverter having equal or unequal capacity and the same or different output. The current is allocated according to the output of each inverter, and the current allocation coefficient is as follows: ；（16） In the formula k i For the first i Current distribution coefficient of each inverter; i i It is the first i The current reference value of the first inverter, with the first i The per-unit value is obtained by taking the rated capacity of each inverter as the base value; m It is the ratio of the rated capacity of the synchronous motor to that of the new energy power station; the ratio of the rated capacity of multiple inverters is... n 1: n 2: n 3: ...: n N , Indicates the first i The rated capacity of each inverter, where N represents the number of inverters.

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