Control method of voltage source type dynamic reactive power compensator based on rotating phase displacement transformer

Abstract

The application discloses a control method of a voltage source type dynamic reactive compensator based on a rotary phase shifting transformer (RPST), and belongs to the field of reactive power compensation of distribution networks. The control method mainly comprises power outer loop control, current inner loop control and an RPST angle generating part. The control method is used for controlling the relative position angle of the primary and secondary windings of two RPSTs to synthesize a voltage vector with adjustable amplitude and phase, adjusting the voltage on both sides of the compensation capacitor of the voltage source type dynamic reactive compensator, and continuously changing the size and direction of the compensation current of the dynamic reactive compensator. The dynamic reactive compensator can realize continuous and bidirectional reactive power compensation, has the advantages of high voltage, large capacity, low harmonic, easy operation and maintenance, low cost, strong impact resistance and the like, and has a higher cost performance for the case of compensating for a single direction inductive load.

Description

Technical Field

[0001] This invention belongs to the field of reactive power compensation technology for distribution networks, and specifically relates to a novel dynamic reactive power compensation system for distribution networks containing nonlinear loads such as distributed renewable energy sources and electric vehicles. Background Technology

[0002] To reduce carbon emissions from electricity production, a large number of distributed renewable energy sources are being integrated into the distribution network, making it no longer a traditional single-flow power distribution network. On the other hand, with the gradual acceleration of electricity substitution, a large number of nonlinear loads such as electric vehicles and air conditioners are being integrated into the distribution network, placing higher demands on the power supply quality of the distribution network. The new distribution network is characterized by a high proportion of distributed renewable energy penetration and a high proportion of nonlinear new loads. These new changes place higher demands on reactive power compensation equipment in the distribution network.

[0003] With the widespread grid connection of distributed renewable energy sources, voltage exceeding limits at grid connection points has become a significant factor affecting the safe and stable operation of distribution networks, leading to increasingly complex power flow patterns. Furthermore, the increasing proportion of nonlinear loads such as electric vehicles and air conditioners is expanding the reactive power demand of distribution networks. If large-scale reactive power flows persist within the distribution network, it will not only increase network losses and reduce transmission capacity, but also cause voltage exceeding limits, impacting the power supply quality. Therefore, a device and control strategy capable of flexibly compensating for the reactive power required by these new distribution networks is needed.

[0004] Traditional Static Var Compensators (SVCs) offer simple structures and low costs, effectively compensating for the reactive power required by the system. However, they only allow for tiered regulation, typically resulting in overcompensation or undercompensation. Furthermore, each capacitor switching introduces a surge response, impacting device lifespan. The use of power electronic devices also injects harmonics into the system, affecting power quality. Static Synchronous Compensators (STATCOMs) provide continuous and precise compensation, significantly improving harmonic performance. However, their overall cost is higher, and considering the tolerance issues of power electronic devices, high-voltage, high-capacity applications are difficult to achieve, hindering widespread adoption in distribution networks. Hybrid SVC and STATCOM systems, operating in series and parallel, leverage their complementary advantages to achieve continuous regulation and reduce costs. SVCs handle large-capacity regulation, while STATCOMs provide small-capacity continuous regulation. However, the surge response from capacitor switching still exists, affecting the overall lifespan of the equipment.

[0005] Therefore, it is necessary to consider a voltage source type dynamic reactive power compensator based on a Rotary Phase Shifting Transformer (RPST) to meet the requirements of new distribution networks for precise adjustment, cost-effectiveness, ease of operation and maintenance, strong impact resistance, and good endurance of reactive power compensation equipment. The RPST-based voltage source type dynamic reactive power compensator has continuous and bidirectional reactive power compensation capabilities. Using RPST instead of power electronic switch bridges effectively reduces equipment costs and facilitates high-voltage and large-capacity applications. The purpose of this invention is to provide a control method specifically suitable for connecting voltage source type dynamic reactive power compensators to new distribution networks, providing dynamic reactive power support. Summary of the Invention

[0006] This invention provides a control method for a voltage source type dynamic reactive power compensator based on RPST. The basic idea is to connect the dynamic reactive power compensator in parallel at the reactive power compensation point to provide a compensation current to the system. By adjusting the phase shift angle of the two RPSTs, the voltage applied across the capacitor is changed according to the vector synthesis principle, thereby continuously changing the magnitude and direction of the compensation current. When the compensation current is exactly equal to the reactive component of the load current, the dynamic reactive power compensator can achieve full compensation of the load reactive power and has continuous and bidirectional reactive power compensation capability.

[0007] To solve the above-mentioned technical problems, the technical solution provided by the present invention is to adopt a dual closed-loop control strategy of power outer loop and current inner loop. Its structure includes a voltage source type dynamic reactive power compensator main circuit based on RPST, a measurement module, a phase-locked loop (PLL), a dq decomposition module, a power calculation module, a power outer loop control module, a current inner loop control module, and an RPST angle generation module. The specific technical method is as follows: First, the grid connection point voltage is fixed as the d-axis by the measurement module and PLL, and all other measured values ​​are decomposed into dq components in this coordinate system. Second, the actual compensated reactive power is obtained from the grid connection point voltage and the compensation current. Then, the reactive power required by the load is used as the command value for the power outer loop control, and the actual compensated reactive power of the dynamic reactive power compensator is used as the feedback value. After PI regulation, the command value of the secondary side reactive current component is calculated. Since the control of the reactive power of the dynamic reactive power compensator is mainly considered, the command value of the active component of the secondary side current is 0. The reactive and active components of the secondary side current obtained by the measurement module and the dq decomposition module are used as the feedback values ​​for the current inner loop control. Finally, the voltage on both sides of the compensation capacitor is obtained according to the secondary side current, and then the phase shift angle corresponding to each of the two RPSTs is obtained by the RPST angle generator. The angle is input into the RPST to change the relative position angle of the primary and secondary windings, and finally the full compensation of reactive power is achieved.

[0008] Compared to existing SVCs (Sequentially Selective Capacitors), dynamic var compensators (RVCs) can achieve continuous reactive power compensation, solving the problems of impact response and inaccurate compensation caused by the staged switching of SVC capacitors, and also avoiding the injection of excessive harmonics into the system. Compared to fast-response reactive power compensation devices (STATCOMs), dynamic RVCs do not require the use of power electronic devices, reducing costs. Using RPSTs eliminates the need to consider the voltage withstand capability of power electronic devices and complex control strategies, allowing for large-scale deployment in distribution networks. Therefore, dynamic RVCs offer multiple advantages, including continuous bidirectional accurate compensation, cost-effectiveness, suitability for high voltage applications, large capacity, ease of operation and maintenance, strong impact resistance, and good resilience, meeting the reactive power compensation needs of new distribution networks. Attached Figure Description

[0009] Figure 1 This is the electrical wiring diagram for a single-phase voltage source type dynamic reactive power compensator based on RPST.

[0010] Figure 2 This is an electrical application diagram of a voltage source type dynamic reactive power compensator based on RPST connected to a power distribution line.

[0011] Figure 3 This is a single-phase equivalent schematic diagram of a voltage source type dynamic reactive power compensator based on RPST connected to a power distribution line.

[0012] Figure 4 This is a single-phase equivalent circuit diagram of a voltage source type dynamic reactive power compensator based on RPST connected to a power distribution line.

[0013] Figure 5 This is a block diagram of a three-phase voltage source type dynamic reactive power compensator control system based on RPST.

[0014] Figure 6 This is a diagram of the dual closed-loop control strategy for a three-phase voltage source type dynamic reactive power compensator based on RPST.

[0015] Figure 7 The power factor on the power supply side of a three-phase voltage source dynamic reactive power compensator based on RPST operating under capacitive conditions when reactive load changes.

[0016] Figure 8 The phase shift angle of the RPST-based three-phase voltage source dynamic reactive power compensator when the reactive load changes under capacitive conditions.

[0017] Figure 9 The power factor on the power supply side of a three-phase voltage source dynamic reactive power compensator based on RPST operating under inductive conditions when reactive load changes.

[0018] Figure 10The phase shift angle of the RPST-based three-phase voltage source dynamic reactive power compensator when the reactive load changes under inductive conditions. Detailed Implementation

[0019] This invention provides a control method for a voltage source type dynamic reactive power compensator based on RPST (Reactive Power Steering). The control method mainly includes three parts: power outer loop control, current inner loop control, and an RPST angle generator. It can be specifically applied to single-phase voltage source type dynamic reactive power compensators or three-phase voltage source type dynamic reactive power compensators based on RPST.

[0020] To explain in detail the control method of the voltage source dynamic reactive power compensator based on RPST, we first introduce the structural principle of the single-phase voltage source dynamic reactive power compensator based on RPST. The structural principle of the three-phase voltage source dynamic reactive power compensator is similar to that of the single-phase compensator.

[0021] Figure 1 This is the electrical wiring diagram for a single-phase voltage source type dynamic reactive power compensator based on RPST (Reactive Power Supply Transformer). It mainly includes a series inductor 1, a dual RPST phase-shifting transformer and its rotor position angle adjustment component 2, and a parallel compensation capacitor 3. The primary windings 4 of the two RPSTs are connected in parallel and connected to the reactive power compensation point via the series inductor 1. The distribution network provides excitation current to the RPSTs, establishing a rotating magnetic field in the primary core 5, secondary core 6, and their air gap. Under this rotating magnetic field, an electromotive force is induced in the primary and secondary windings 4 and 7. The amplitude depends on the number of turns, and the phase depends on the relative position angles 8 and 9 of the primary and secondary windings. The secondary windings 7 of the two RPSTs are connected in series and then connected to both sides of the compensation capacitor 3. According to the principle of vector synthesis, by adjusting only the phase shift angles 8 and 9 of the two RPSTs, the voltage amplitude and phase on both sides of the compensation capacitor 3 can be continuously adjusted.

[0022] Figure 2 This diagram illustrates the electrical application of a voltage source dynamic reactive power compensator (RPST) connected to a distribution line. The RPST-based RPST RPST is connected in parallel between the system's equivalent power source and the load. The end load can be an electrical load, a distributed renewable energy source, or a combination of both in any capacity ratio. Single-phase voltage source dynamic reactive power compensators connected to distribution lines are suitable for compensating for reactive power deficits caused by single-phase nonlinear users, reducing reactive power flow, and improving three-phase imbalances caused by single-phase loads. Three-phase voltage source dynamic reactive power compensators connected to the distribution network are suitable for distributed renewable energy grid connection and the connection of new loads such as electric vehicles and air conditioners, improving the transmission capacity and power quality of the distribution network and contributing to its economical and stable operation.

[0023] Figure 3This is the single-phase equivalent circuit diagram of a voltage source dynamic reactive power compensator (RPST) connected to a power distribution line. The internal resistance of the RPST is ignored, and its internal inductance is included in the series inductance, denoted by L′. System equivalent power supply. To the equivalent impedance Z L The end load is supplied with power, and the load current is The ratio of the primary to secondary windings of the RPST is T. RPST Here, we can take 0.5. The relative position angles of the primary and secondary windings are α1 and α2, respectively. The voltage across the composite compensation capacitor is... The compensation current of the dynamic reactive power compensator is When the compensation current Just enough to compensate for the load current When the reactive component is in the middle, full reactive power compensation can be achieved.

[0024] The relationship between the primary and secondary voltages of RPST can be expressed as:

[0025]

[0026] According to the principle of vector composition, the voltage across the capacitor is:

[0027]

[0028] To simplify the control method, let T be taken. RPST =0.5, δ = (α1-α2) / 2 and Then equation (2) can be transformed into:

[0029]

[0030] Let α1 = -α2 = α, then equation (3) can be expressed as:

[0031]

[0032] Figure 4 This is the single-phase equivalent circuit diagram of a voltage source dynamic reactive power compensator (RPST) connected to a power distribution line. The compensation current of the voltage source dynamic reactive power compensator is expressed as:

[0033]

[0034] The reactive power generated by the compensation capacitor C is expressed as:

[0035]

[0036] The reactive power absorbed by the series inductor L′ is expressed as:

[0037] Q l =I 2 ωL′ (7)

[0038] Therefore, the reactive power compensation of a dynamic reactive power compensator can be expressed as:

[0039] Q = Q l -Q c (8)

[0040] Substituting equations (4), (5), (6), and (7) into equation (8), we can simplify and approximate the result as follows:

[0041]

[0042] From equation (9), it can be seen that when When Q < 0, the phase shift angle α of RPST is relatively small. When the amplitude is large, the reactive power generated by the capacitor is greater than the reactive power absorbed by the inductor. The dynamic reactive power compensator then outputs reactive power to compensate for the inductive load. When Q > 0, the phase shift angle α of RPST is relatively large. When the amplitude is small, the reactive power absorbed by the inductor is greater than that absorbed by the capacitor. The dynamic reactive power compensator absorbs reactive power from the outside, which can compensate for capacitive loads.

[0043] Figure 5 This is a block diagram of a three-phase voltage source type dynamic reactive power compensator control system based on RPST. The measurement module measures the voltage at the parallel connection point. Compensation current and secondary current By PLL Fixed as the d-axis, in this dq coordinate system, for Decomposition was performed to obtain the dq components of each phase. and The power outer loop control selects the reactive power required by the load as the reactive power command value Q. ref The actual reactive power compensated by the dynamic reactive power compensator is the feedback value Q, obtained from the power calculation module. The reactive power outer loop control output is the command value of the secondary side reactive current component. Since the impact of dynamic reactive power compensators on active power is not considered here, the command value of the secondary active current component is... Setting it to 0 will reduce the active component of the secondary current output by the measurement module. reactive power The command value of the output capacitor voltage is used as the input current of the inner loop control module as feedback. The RPST angle generator is composed of The phase shift angle α of the two RPSTs is obtained and input into the RPST phase shift voltage regulation module to achieve full compensation of reactive power of the load and maintain the power factor on the power supply side at the set value.

[0044] Figure 6 This diagram illustrates a dual-closed-loop control strategy for a three-phase voltage source dynamic reactive power compensator based on RPST (Reactive Power Stress Test). It mainly comprises three parts: power outer loop control, current inner loop control, and RPST angle generation. The power outer loop control selects the reactive power on the load line as the reactive power command value Q. ref The actual reactive power compensation of the dynamic reactive power compensator is used as the feedback value Q, which is then processed by a PI regulator to achieve Q-to-Q feedback. ref The tracking control outputs a reactive power command value from the output capacitor. according to Obtain the command value of the secondary side reactive current component. The inner-loop current control is divided into secondary-side active current control and secondary-side reactive current control. This control strategy does not consider the control of the active part of the dynamic reactive power compensator, therefore the active current command value... When set to 0, the output of the outer power loop is the reactive current command value. The dq component of the actual secondary current is used as the feedback value. Each is achieved through a PI controller. right right Tracking control is implemented. To ensure that the secondary current does not exceed the rated current, a limiting circuit is added, with the limit set at 1.1 times the rated secondary current. The dq component of the current is converted into current amplitude and phase. The reference voltage value across the capacitor is obtained from the capacitor's volt-ampere characteristic relationship. Since the secondary current is predominantly q-axis, the capacitor voltage is located near the d-axis. Phase correction is used to obtain the commanded capacitor voltage value on the d-axis. The RPST angle generator is based on the primary side voltage. and capacitor voltage command value The phase shift angles of the two RPSTs were calculated to be α1 = -α2 = α.

[0045] according to Figure 2 Electrical application diagram of RPST-based voltage source dynamic reactive power compensator connected to power distribution line and Figure 3 An equivalent schematic model of a voltage source type dynamic reactive power compensator (RPST) connected to a power distribution line was constructed, and the system simulation parameters are shown in Table 1. The designed adjustment range of the dynamic reactive power compensator is -1MVar to 1MVar, with the absorption of reactive power as the positive value.

[0046] Table 1 Simulation System Parameters

[0047]

[0048] The initial inductive load of the line is set to 0.3 MVar, increased to 0.6 MVar at 5 seconds, and further increased to 1 MVar at 10 seconds. At this time, the dynamic reactive power compensator operates under capacitive conditions, and the power factor on the power supply side is as follows: Figure 7As shown in the figure, when the reactive load increases for the first time, the power factor drops to 0.960, a decrease of approximately 4%, and recovers to its steady-state value before the load increase after 0.511 seconds. When the reactive load increases for the second time, the power factor drops to 0.933, a decrease of approximately 6.7%, and recovers to its steady-state value before the load increase after 0.537 seconds. The RPST phase shift angle is shown below. Figure 8 As shown, with each fluctuation in reactive load, the power factor recovers to 1 within approximately 0.5 seconds, demonstrating the good adjustment characteristics of the dynamic reactive power compensator within the capacitive compensation range.

[0049] The initial capacitive load of the line is set to 0.3 MVar, increased to 0.6 MVar at 5 seconds, and further increased to 1 MVar at 10 seconds. At this time, the dynamic reactive power compensator operates under inductive conditions, and the power factor on the power supply side is as follows: Figure 9 As shown in the figure, when the reactive load increases for the first time, the power factor drops to 0.958, a decrease of approximately 4.2%, and recovers to its steady-state value before the increase in reactive load after 0.528 seconds. When the reactive load increases for the second time, the power factor drops to 0.9290, a decrease of approximately 7.1%, and recovers to its steady-state value before the increase in reactive load after 0.577 seconds. The RPST phase shift angle is shown below. Figure 10 As shown, with each fluctuation in reactive load, the power factor recovers to 1 within approximately 0.5 seconds, demonstrating the good regulation characteristics of the dynamic reactive power compensator within the inductive compensation range.

[0050] As described above, the present invention has been described in detail. Obviously, the present invention is not limited to the given embodiments. Any modifications that can be made by those skilled in the art without substantially departing from the inventive point and effect of the present invention are also included within the protection scope of the present invention.

Claims

1. A control method of a voltage source type dynamic reactive power compensator based on a rotary phase shifting transformer (RPST), which belongs to the technical field of distribution network reactive power compensation and is suitable for dynamic reactive power compensation of a distribution network containing distributed new energy and electric vehicle nonlinear loads; the control method of the voltage source type dynamic reactive power compensator comprises a power outer loop control, a current inner loop control and an RPST angle generation part. The RPST angle generating part generates the phase shift angle α1, α2 according to the capacitor voltage command value outputted by the current inner loop control part and RPST primary side voltage The phase shift angles α1, α2 of the two RPSTs are obtained; since the capacitor voltage command value is located in the +d-axis direction, and the system loss of the RPST can be ignored, is located in the +d-axis, thus α1=-α2=α, inputting α into the RPST, giving the relative position angle of the primary and secondary windings, and synthesizing the capacitor voltage to precisely compensate the required reactive power of the load.

2. In the control method according to claim 1, the power outer loop control section first measures the parallel point voltage using a measurement module. and compensation current And The d-axis is controlled by a PLL in the dq rotating coordinate system, and then obtained through the dq decomposition module. The reactive power Q required by the load ref As the reactive power command value for the outer loop power control, and The actual reactive power Q compensated by the dynamic reactive power compensator can be calculated and used as the reactive power feedback value for the power outer loop control. This feedback value is then used by the PI regulator to obtain the command value for the reactive power output by the capacitor. This leads to the secondary reactive current component.

3. The control method of claim 1, the inner current loop control part, first, the secondary side current is measured by the measurement module The dq decomposition module obtains Since the control strategy does not consider the active part of the dynamic reactive power compensator, the active component command value of the secondary side current Is always 0, the reactive component command value of the secondary side current Is the output of the power outer loop control part; And The feedback values of the active component and the reactive component of the secondary side current are respectively realized by PI regulators To realize tracking control of To realize tracking control of The amplitude limiting module takes 1.1 times the rated current of the secondary side, and the amplitude |U c And the phase θ u Of the capacitor voltage are obtained through amplitude-angle conversion and calculation, and the d-axis capacitor voltage command value is obtained after phase correction

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