Medium voltage uninterruptible power supply system and control method based on cascade super-capacity energy storage

Abstract

The present invention relates to power electronics and energy storage technology, and aims to provide a medium-voltage uninterruptible power supply system and control method based on cascaded super-capacitor energy storage. The system uses a three-phase cascaded super-capacitor energy storage module, which is connected to the isolation reactor and the load-side switch through a filter reactor to stabilize the load bus voltage. The present invention uses adaptive power reference calculation, voltage phase control, and voltage amplitude stabilization control operations; fully considers the super-capacitor wide voltage operating characteristics, and adaptively adjusts the control of the super-capacitor charging and discharging process according to the grid fault state and the super-capacitor voltage deviation, so that the system can provide the required power support in the event of a fault, and smoothly replenish energy after recovery, which helps to avoid risks such as super-capacitor voltage exceeding the limit, and improves the effectiveness of energy management and the stability of the system. During a grid fault, the load voltage is restored to near the rated value in a relatively short time, reducing voltage drops and overshoots, and enhancing the system response speed and voltage support capability.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics and energy storage technology, and particularly relates to a medium-voltage uninterruptible power supply system based on cascaded super-capacitor energy storage and a control method. Background Art

[0002] In recent years, highly sensitive industrial loads, typically represented by precision manufacturing, data centers, and mineral mining, have placed stringent demands on the reliability of medium-voltage power grids. Voltage sags (typically lasting milliseconds to seconds), the most common power quality issue, can cause major incidents such as equipment downtime and production line paralysis, resulting in immeasurable economic losses. While existing dual-circuit power supply systems can provide basic protection through backup bus switching, delays in switch operation lead to unavoidable power interruptions during the switching process, making it difficult to achieve millisecond-level uninterruptible power supply. Traditional uninterruptible power supplies, limited by voltage and power levels, are only suitable for low-voltage scenarios (typically less than 1 kV) and cannot meet the megawatt-level power supply demands of large-capacity medium-voltage loads (typically 6 to 35 kV).

[0003] To address this technical bottleneck, researchers have proposed various medium-voltage uninterruptible power supply (MVUPS) solutions. However, these solutions share a common challenge: they require a step-up transformer at the topology level, introducing additional losses (efficiency loss of approximately 1-2%), and transformer leakage inductance can affect voltage control accuracy. Furthermore, to meet the power demands of large-capacity loads, low-voltage battery energy storage systems require multiple units in parallel and complex coordinated control, which can lead to stability issues. Furthermore, the series-parallel configuration of batteries on the DC side makes it difficult to avoid circulating currents between cells and can easily lead to localized accelerated aging, threatening overall system reliability. To address these limitations of battery energy storage, supercapacitors (referred to as "supercapacitors" in this document) can effectively meet the short-term high-power support requirements during voltage sags due to their superior characteristics, such as ultra-long cycle life, high power density, and millisecond-level response time. This holds great potential for application in MV UPS systems, promising faster dynamic response, lower investment costs, and a smaller footprint.

[0004] However, due to the wide range of variations and rapid dynamic characteristics of supercapacitors during charging and discharging, integrating supercapacitors with medium-voltage uninterruptible power supply systems places special and stringent demands on the control system in terms of rapid response and energy management. Existing public literature suggests that researchers have generally failed to pay sufficient attention to this issue, and no targeted solutions have yet been identified. Attempting to directly apply existing control methods to this system may face the following key technical issues:

[0005] 1. Existing control strategies are often based on design experience with battery energy storage systems with relatively constant DC voltages, and fail to fully consider the wide range of variations in overcapacity during charging and discharging. Currently, there is a lack of solutions that adaptively adjust charging and discharging strategies based on the overcapacity's real-time voltage and system operating conditions. This results in suboptimal discharge when power support is needed, and inefficiency and poor stability during recharging, making effective adaptive energy management of overcapacity impossible.

[0006] 2. Existing control strategies usually do not take the load voltage amplitude as a direct optimization target, and lack an active suppression mechanism for fault transient impacts and system oscillations. As a result, it is difficult for the system to balance response speed and voltage stability. The final manifestation is a significant drop or overshoot in the voltage amplitude, which may be accompanied by a long period of oscillation before stabilization, and cannot meet the power supply quality requirements of highly sensitive loads.

[0007] Therefore, there is an urgent need to develop a new medium-voltage uninterruptible power supply system based on cascaded super-capacity energy storage and its control method to overcome the limitations of existing solutions, realize adaptive management of super-capacity energy and fast, precise and stable control of load voltage, so as to meet the stringent requirements of medium-voltage highly sensitive loads for power supply continuity and stability. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the shortcomings of the existing technology and provide a medium-voltage uninterruptible power supply system and control method based on cascaded supercapacitor energy storage. This solution aims to achieve rapid and stable control of load voltage and ensure efficient and adaptive management of supercapacitor energy.

[0009] To solve the technical problem, the solution of the present invention is:

[0010] First, a control method for a medium voltage uninterruptible power supply based on cascaded super-capacity energy storage is provided, comprising the following steps:

[0011] S201, adaptive power reference calculation

[0012] Collect three-phase voltage on the grid side u gx , three-phase voltage on the load side v x And the three-phase output current of the cascaded super-capacitor energy storage module i x , x=a , b , c (referring to the three phases of AC respectively); according to the voltage v x and current i x , calculate the load voltage amplitude V m, cascaded super-capacity energy storage modules output active power P ; Collect the supercapacitive voltage of each submodule in the cascade supercapacitive energy storage module U sc,xj , j= 1,2,…, N , calculate the average overcapacitance voltage U SCavg ; Calculate the active power reference value of the cascaded super-capacity energy storage module based on the grid fault status and the super-capacity average voltage P ref ;

[0013] S202, voltage phase control

[0014] According to the active power reference value P ref , generating a voltage phase reference value through the voltage phase control law to adjust the output phase of the cascaded super-capacitor energy storage module;

[0015] S203, voltage amplitude stabilization control

[0016] The modulation voltage reference value is generated by the dynamic damping voltage control law and the voltage amplitude control law to drive the cascaded super-capacitor energy storage module to stabilize the load voltage amplitude.

[0017] As a preferred solution of the present invention, in step S201, the average over-capacity voltage is calculated by dividing the sum of the over-capacity voltages of each submodule by the total number of submodules. U SCavg , as shown in the following formula:

[0018] ;

[0019] in, N is the number of submodules in each phase, j= 1,2,…, N ; U sc,aj 、 U sc,bj 、 U sc,cj They are the overcapacity voltage of each submodule in the three phases.

[0020] As a preferred solution of the present invention, in step S201, the active power reference value of the cascaded super-capacity energy storage module is calculated according to the following formula: P ref :

[0021] ;

[0022] in, P SC It is the reference value of active power for over-capacity voltage stabilization; POutput active power for cascaded super-capacity energy storage modules; F It is the grid temporary sag fault state value, and its judgment condition is: when the grid voltage amplitude fluctuation range exceeds ±10%, F =1; otherwise, F =0.

[0023] As a preferred solution of the present invention, the over-capacity voltage-stabilized active power reference value P SC The calculation formula is as follows:

[0024] ;

[0025] in, It is the over-capacity charging and discharging active power limit, which is used to limit the over-capacity charging and discharging power value; k SC is the excess power ratio coefficient;

[0026] Δ U SC is the over-capacity voltage deviation value, which is calculated as follows:

[0027] ;

[0028] in, U SCref is the overcapacitance voltage reference value, U SCavg is the average overcapacitance voltage.

[0029] As a preferred solution of the present invention, in step S202, the voltage phase control law is as follows:

[0030] ;

[0031] in, θ ref is the voltage phase reference value; s is the Laplace operator; ω 0 is the rated angular frequency of the load;

[0032] Δ ω is the angular frequency correction, and its calculation formula is as follows:

[0033] ;

[0034] in, s is the Laplace operator; ω c is the voltage phase control cut-off frequency; m is the voltage phase control proportional coefficient.

[0035] As a preferred solution of the present invention, step S203 includes two steps: dynamic damping voltage calculation and voltage amplitude control, specifically including:

[0036] S2031, Dynamic Damping Voltage Calculation

[0037] The dynamic damping voltage is used to eliminate the oscillation risk caused by transient impact disturbances; the d-axis and q-axis dynamic damping voltages are calculated according to the dynamic damping voltage control law. v zd and v zq , the specific calculation formula is as follows:

[0038] ;

[0039] in, s is the Laplace operator; ω z Control the cutoff frequency for dynamic damping; i d and i q are the d-axis and q-axis output currents respectively; k z is the high-pass filter proportional coefficient; r z is the damping coefficient;

[0040] S2032, voltage amplitude control

[0041] The voltage amplitude control law is used to achieve stable control of the load voltage amplitude. The specific calculation formula is as follows:

[0042] ;

[0043] in, m d and m q Represent the d-axis and q-axis modulation voltage reference values respectively; s is the Laplace operator, k pv is the load voltage control proportional coefficient; k iv is the load voltage control integral coefficient; V ref is the load voltage amplitude reference; V m is the load voltage amplitude;

[0044] Then use the voltage phase reference θ ref , d-axis modulation voltage reference value m d and q-axis modulation voltage reference valuem q Perform inverse coordinate transformation to obtain the three-phase modulation voltage reference value m a , m b , m c ;use m a , m b , m c Modulate and drive the cascaded super-capacity energy storage module to operate.

[0045] As a preferred solution of the present invention, according to the commissioning status of the cascaded super-capacity energy storage module, the medium voltage uninterruptible power supply system is operated in the following manner:

[0046] (1) When the cascaded super-capacity energy storage module is able to operate normally, the medium voltage uninterruptible power supply system operates in a voltage stabilization mode; in this mode, the load side switch S 1 and grid-side switches S 2 In closed state, bypass switch S 3 is in disconnected state; and by executing the steps to control the operation of the cascaded super-capacity energy storage module, a stable load voltage is achieved;

[0047] (2) When the cascaded super-capacity energy storage module fails and is removed, the medium voltage uninterruptible power supply system operates in bypass mode: in this mode, the load side switch S 1 and grid-side switches S 2 In the disconnected state, the bypass switch S 3 In the closed state, the load is directly powered by the grid.

[0048] The present invention further provides a medium voltage uninterruptible power supply system based on cascade super-capacitor energy storage, which applies the above-mentioned medium voltage uninterruptible power supply control method based on cascade super-capacitor energy storage. The system includes: an isolation reactor L i , filter reactor L f , cascaded super-capacitor energy storage modules, load-side switches S 1 , grid-side switch S 2 , bypass switch S 3 and a controller; the load side switch S 1 , Isolation ReactorL i , grid-side switch S 2 Connected in series between the load and the grid, and connected to the bypass switch S 3 Parallel connection; the cascaded super-capacitor energy storage module is connected through a filter reactor L f Connect to the isolation reactor L i With load side switch S 1 Between; Among them, the isolation reactor L i Used to limit fault current during grid faults, cascaded super-capacitor energy storage modules are used to stabilize load bus voltage, filter reactors L f Used to suppress the output harmonics of the cascaded super-capacitor energy storage module; the controller is configured to execute the control method;

[0049] The cascade super-capacity energy storage module is a three-phase structure, each phase consists of N The submodules of the same structure are connected in series. Each submodule includes a supercapacitor, a filter capacitor and an H-bridge converter connected in parallel. The supercapacitor is referred to as a supercapacitor. The number of submodules in each phase of the cascade supercapacitor energy storage module is N The capacity of the submodule and the excess capacity are configured according to the actual demand of the power supply power and power supply duration of the medium voltage load.

[0050] Description of the invention principle:

[0051] 1. The present invention uses adaptive power reference adjustment based on fault status and over-capacity voltage deviation to enable the system to meet power requirements while maintaining the over-capacity voltage within a reasonable operating range, avoiding problems such as over-capacity voltage exceeding the limit that may be caused by conventional control methods, and achieving optimized energy management.

[0052] 2. The present invention controls the voltage phase and combines adaptive power reference calculation. When the power grid is normal, the over-capacity voltage is controlled to a given over-capacity voltage reference value. U Scref During a grid sag, the cascaded supercapacitor energy storage module will automatically discharge to provide power support for the load; after the fault is cleared, the supercapacitor voltage will smoothly recover to U SCref Through this voltage phase control link, the system active power can accurately track its reference value, thereby completing the management of excess energy and ensuring that the system output voltage remains synchronized with the grid voltage during grid-connected operation.

[0053] 3. Voltage amplitude stabilization control includes dynamic damping control and voltage amplitude control, both of which are θ ref The dynamic damping voltage is used to eliminate the risk of oscillation caused by disturbances such as transient shocks, and the voltage amplitude control law is used to achieve stable control of the load voltage amplitude.

[0054] This invention utilizes voltage amplitude stabilization control to establish a closed-loop control system with the load voltage amplitude as direct feedback. This system can quickly and accurately correct amplitude deviations, ensuring that the load voltage amplitude accurately tracks the reference. Simultaneously, a dynamic damping voltage is introduced to generate a compensation voltage signal with an opposite oscillation trend, which is superimposed on the modulation command to actively suppress system oscillations during transient states. Its high-pass characteristics improve the system's dynamic voltage stability without compromising steady-state voltage accuracy.

[0055] 4. The medium-voltage uninterruptible power supply system based on cascaded super-capacity energy storage of the present invention has two operating modes: voltage stabilization mode and bypass mode. Normally, the medium-voltage uninterruptible power supply system operates in voltage stabilization mode, providing stable power to the load. In the event of a system shutdown, such as a failure of the cascaded super-capacity energy storage module, the medium-voltage uninterruptible power supply system operates in bypass mode. When the cascaded super-capacity energy storage module is shut down, the load is powered directly by the grid.

[0056] 5. The controller of the system described in the present invention includes a processor and a computer-readable storage medium, and a computer program is stored on the computer-readable storage medium; when the computer program is executed by the processor, it can realize the adaptive power reference calculation, voltage phase control and voltage amplitude stabilization control.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] 1. The control method of the medium-voltage uninterruptible power supply system based on cascaded super-capacity energy storage in the present invention fully considers the super-capacity wide voltage operating characteristics through adaptive power reference calculation, and adaptively adjusts the control of the super-capacity charging and discharging process according to the grid fault state and the super-capacity voltage deviation, so that the system can provide the required power support in the event of a fault and perform smooth energy replenishment after recovery, which helps to avoid risks such as super-capacity voltage limit violations and improve the effectiveness of energy management and the stability of the system.

[0059] 2. The present invention is based on a control method for a medium-voltage uninterruptible power supply system with cascaded super-capacitor energy storage. Through a voltage amplitude stabilization control strategy, the load voltage amplitude error is used as a direct feedback signal to achieve high-precision closed-loop control. At the same time, the dynamic damping voltage calculation and compensation mechanism introduced actively generates damping based on the high-frequency information of the output current to suppress system oscillations during disturbances. Due to its high-pass filtering characteristics, this damping link mainly acts on transients without affecting steady-state accuracy. During a grid fault, the rapid adjustment of this strategy can restore the load voltage to near the rated value in a relatively short period of time, reducing voltage drops and overshoots.

[0060] 3. The system of the present invention adopts a cascade converter topology. The cascaded supercapacitor energy storage module does not require a step-up transformer to be directly connected to the medium-voltage power grid. This design avoids the adverse effects of transformer-related losses and leakage inductance. Its sub-modular architecture facilitates the expansion of power levels on demand, improving the applicability of the system. At the same time, supercapacitors are selected as energy storage media, and their fast response characteristics are utilized to enhance the system's response speed and voltage support capabilities to transient events such as voltage sags. Combined with the high power density characteristics of supercapacitors, this system solution helps to optimize investment costs and equipment space in short-term, high-power voltage sag control scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a topology diagram of the medium-voltage uninterruptible power supply system based on cascaded super-capacity energy storage in the present invention.

[0062] Figure 2 It is a control block diagram of the method for realizing medium voltage uninterruptible power supply of the present invention.

[0063] Figure 3 The figure shows waveforms of multiple load and grid parameters when the control method of the present invention is used when the three-phase grid voltage temporarily drops to 10%.

[0064] Figure 4 The following are waveform diagrams of multiple parameters of the cascaded super-capacity energy storage module using the control method of the present invention when the three-phase grid voltage temporarily drops to 10%. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further clearly and completely described below in conjunction with the accompanying drawings and embodiments. It should be understood that the described embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Any modification or equivalent substitution made to the present invention under the guidance of the present invention, or any product similar to the present invention obtained by combining the present invention with other technical features, falls within the scope of protection of the present invention.

[0066] 1. Overview of the implementation scheme of the present invention

[0067] 1.1 Topology of Medium Voltage Uninterruptible Power Supply System

[0068] Figure 1 This is a topology diagram of the medium-voltage uninterruptible power supply system with cascaded super-capacity energy storage in the present invention. The topology of the system and the structure of the cascaded super-capacity energy storage module are as described above.

[0069] 1.2 How Cascaded Super-Capacity Energy Storage Modules Work

[0070] Cascaded supercapacitor energy storage modules generate the required AC voltage to stabilize the load bus according to control commands. After receiving a control signal from the controller, each submodule operates its own supercapacitor via an internal H-bridge converter. Specifically, the control signal instructs the H-bridge to switch, selectively applying the supercapacitor voltage (typically forward voltage, reverse voltage, or zero voltage) to the circuit formed by all the submodules in series for that phase.

[0071] In the same phase of the cascaded supercapacitor energy storage module, modulation techniques suitable for cascaded H-bridge converters, such as carrier phase-shift pulse width modulation or carrier stacked pulse width modulation, are used to enable the voltages output by all submodules to be superimposed in series to synthesize a multi-level step voltage that approximates the target waveform. Finally, the multi-level step voltage output by the cascaded supercapacitor energy storage system passes through the filter reactor. L f After filtering, the load bus voltage is constructed, and by precisely controlling the input or bypass of each sub-module, dynamic, rapid adjustment and stabilization of the load bus voltage amplitude and phase are achieved.

[0072] 1.3 Based on the commissioning of the cascaded super-capacity energy storage modules, the medium-voltage uninterruptible power supply system has two operating modes: voltage stabilization mode and bypass mode. The specific operating mode is as described above.

[0073] Based on common understanding, the controller of the medium-voltage uninterruptible power supply system includes a processor and a computer-readable storage medium, and a computer program is stored on the computer-readable storage medium; when the computer program is executed by the processor, it can implement the control method of the medium-voltage uninterruptible power supply to be described below in the present invention.

[0074] 1.4 Control Methods for Medium Voltage Uninterruptible Power Supply

[0075] Figure 2 This is a control block diagram of the medium-voltage uninterruptible power supply system based on cascaded supercapacitor energy storage, as described in the present invention. This diagram illustrates the control method described in the present invention, which primarily includes three components: adaptive power reference calculation, voltage phase control, and voltage amplitude stabilization control. The specific implementation is as described above.

[0076] When using the three-phase modulation voltage reference value for modulation, a modulation technique suitable for cascaded H-bridge converters can be adopted, such as carrier phase-shift pulse width modulation or carrier stacked pulse width modulation. Taking carrier phase-shift pulse width modulation as an example, for each phase N Submodule generation N A uniformly phase-shifted triangular carrier. In each submodule, the corresponding modulation voltage reference value (such as m a ) is compared with its triangular carrier, and the comparison result is used to generate the gate pulse signal that drives the H-bridge switch tube of the submodule. The H-bridge of each submodule operates according to the received gate signal, selectively connecting its internal supercapacitor (forward, reverse or bypass) to the series circuit. The output voltages of each submodule in the same phase are superimposed in series to form a multi-level step voltage that is close to a sine wave. After passing through the filter reactor, L f After filtering, the load bus voltage is constructed. Accurately adjust the voltage amplitude through stable control m a , m b , m c , and ultimately achieve the control of the load bus voltage amplitude and phase.

[0077] 2. A specific implementation example and verification results

[0078] In this embodiment, the circuit topology and control model of the medium voltage uninterruptible power supply system are first constructed using PLECS simulation software with reference to the above-mentioned content, in order to verify the specific feasibility and corresponding technical effects of the present invention.

[0079] The relevant operating conditions in the simulation model are set as follows: the grid is a 10 kV / 50 Hz medium voltage grid; the load is a 10 kV / 50 Hz / 4 MW medium voltage load; the rated power of the cascaded super-capacity energy storage module is 5 MW, and the number of sub-modules per phase is N There are 15 submodules, and the overcapacitance value of each submodule is 10 F, which meets the power demand of 5 MW discharge for 25 seconds; filter reactor L f 8 mH; Isolation Reactor L i is 63 mH.

[0080] S201, adaptive power reference calculation

[0081] Collect three-phase voltage on the grid side u gx (In this application x=a , b , c ), three-phase voltage on the load side vx And the three-phase output current of the cascaded super-capacitor energy storage module i x ;according to v x and i x , calculate the load voltage amplitude V m , cascaded super-capacity energy storage modules output active power P . Collect the overcapacity voltage of each submodule U sc,xj ( j= 1,2,…, N ), calculate the average overcapacity voltage of the cascaded overcapacity energy storage module U SCavg .

[0082] According to the grid voltage fault status and over-capacity average voltage U SCavg , calculate the active power reference value of the cascaded super-capacity energy storage module P ref :

[0083] ;

[0084] in, P SC It is the reference value of active power for over-capacity voltage stabilization; P Output active power for cascaded super-capacity energy storage modules; F It is the grid temporary sag fault state value, and its judgment condition is: when the grid voltage amplitude fluctuation range exceeds ±10%, F =1; otherwise, F =0.

[0085] Over-capacity voltage-stabilized active power reference value P SC , the calculation formula is as follows:

[0086]

[0087] in, The active power limit for over-capacity charging and discharging is set to 1 MW; k SC is the excess power ratio coefficient, set to 8500; Δ U sc is the over-capacity voltage deviation value, and the calculation formula is as follows:

[0088] ;

[0089] in, U SCref is the overcapacity voltage reference value, set to 990 V.

[0090] Through adaptive power reference calculation, the system can autonomously adjust the active power reference value P ref , in order to achieve continuous stability of load voltage and automatic management of over-capacity voltage.

[0091] S202, voltage phase control

[0092] Calculate the voltage phase reference value of the cascaded super-capacitor energy storage module through the voltage phase control law θ ref The voltage phase control law is shown in the following formula:

[0093] ;

[0094] in, s is the Laplace operator; ω 0 is the rated angular frequency of the load, which is 100π rad / s; Δω is the angular frequency correction, which is calculated as follows:

[0095] ;

[0096] in, s is the Laplace operator; ω c is the voltage phase control cutoff frequency, set to 200π rad / s; m is the voltage phase control proportional coefficient, which is set to 7.53×10 -6 .

[0097] Through voltage phase control and combined with the adaptive power reference calculation described in step S201, when the grid is normal, the overcapacitance voltage is controlled to 990 V. During a grid sag fault, the overcapacitance will automatically discharge to provide power support to the load. After the fault is cleared, the overcapacitance voltage will smoothly recover to 990 V.

[0098] S203, voltage amplitude stabilization control

[0099] The voltage amplitude stabilization control includes dynamic damping control and voltage amplitude control, both of which are θ ref It is implemented in the defined dq coordinate system.

[0100] S2031, Dynamic Damping Voltage Calculation

[0101] The dynamic damping voltage is used to eliminate the oscillation risk caused by disturbances such as transient shocks. The dynamic damping voltages of the d-axis and q-axis are calculated according to the dynamic damping voltage calculation formula. v zd and v zq, and its calculation formula is:

[0102] ;

[0103] in, s is the Laplace operator; ω z The cutoff frequency for dynamic damping control is set to 20π rad / s; i d and i q are the d-axis and q-axis output currents respectively; k z is the high-pass filter proportional coefficient, set to 1.2; r z is the damping coefficient, set to 28.

[0104] S2032, voltage amplitude control

[0105] The load voltage amplitude is stably controlled by the voltage amplitude control law, which is as follows:

[0106] ;

[0107] in, s is the Laplace operator, k pv is the load voltage control proportional coefficient, set to 0.5; k iv is the load voltage control integral coefficient, set to 7500; V ref is the load voltage amplitude reference, set to 8163.97 V; m d and m q Represent the d-axis and q-axis modulation voltage reference values respectively. θ ref 、 m d and m q Perform inverse coordinate transformation to obtain the three-phase modulation voltage reference value m a , m b , m c ;use m a , m b , m c Modulation is performed. In this embodiment, a carrier phase shift modulation method is used as an example to drive the cascaded super-capacitor energy storage module to operate.

[0108] Figure 3 The following diagram shows the load and grid voltage amplitude, three-phase grid voltage, three-phase load voltage, and three-phase load current waveforms when the three-phase grid voltage temporarily drops to 10% using the control method of the present invention. The grid voltage in the simulation is set as follows: from 0 to 1 second, the grid voltage is normal; at 1 second, the three-phase grid voltage experiences a severe drop to 10%; and at 1.5 seconds, the grid voltage recovers.

[0109] from Figure 3 It can be seen that when the grid voltage is normal, the system operates stably and the load voltage is stable at the rated value; during the entire process of a severe grid voltage drop fault, the load voltage is not interrupted and the load voltage amplitude can be stable at the rated value; when a grid voltage drop fault occurs and when the grid voltage recovers, the load voltage amplitude only fluctuates slightly, with the maximum fluctuation amplitude not exceeding ±5%, and the fluctuation is reduced to within ±1% within one power frequency cycle.

[0110] Figure 4 Is with Figure 3 The waveforms of the load and grid voltage amplitude, output power, output current and average voltage of the cascaded super-capacitor energy storage module using the control method of the present invention under the same simulation. Figure 4 It can be seen that when the grid voltage is normal, the overcapacitor voltage is stable at the set value of 990 V, and the cascaded overcapacitor energy storage module provides reactive power to stabilize the load voltage. When a grid voltage drop fault occurs, the cascaded overcapacitor energy storage module quickly provides power support, and the overcapacitor automatically discharges to stabilize the load voltage. When the grid voltage recovers, the cascaded overcapacitor energy storage module quickly adjusts power to stabilize the load voltage, while the overcapacitor smoothly charges and recovers to 990 V.

[0111] In summary, the medium-voltage uninterruptible power supply system and control method based on cascaded supercapacitor energy storage proposed in this invention achieves continuous load voltage stability under both steady-state and transient conditions, as well as adaptive management of supercapacitor voltage. During severe grid sags, the system rapidly stabilizes load voltage without requiring switching, effectively suppressing voltage fluctuations and ensuring the continuity and stability of power supply to sensitive medium-voltage loads.

Claims

1. A control method for medium voltage uninterruptible power supply based on cascaded super-capacitor energy storage, characterized in that: The following steps are involved: S201, adaptive power reference calculation Collect the three-phase voltage u on the grid side gx , three-phase voltage v on the load side x And the three-phase output current i of the cascaded super-capacitor energy storage module x ,x=a,b,c;according to voltage v x and current i x , calculate the load voltage amplitude V m , the cascaded super-capacity energy storage module outputs active power P; collects the super-capacity voltage U of each sub-module in the cascaded super-capacity energy storage module sc,xj , j=1,2,…,N, calculate the average overcapacitance voltage U SCavg ; Combined with the grid fault status and the average overcapacity voltage, calculate the active power reference value P of the cascaded overcapacity energy storage module ref ; The active power reference value P of the cascaded super-capacity energy storage module is calculated according to the following formula: ref : Among them, P SC is the reference value of the overcapacity voltage-stabilized active power; P is the output active power of the cascaded overcapacity energy storage module; F is the grid sag fault state value, and its judgment condition is: when the grid voltage amplitude fluctuation range exceeds ±10%, F = 1; otherwise, F = 0; The over-capacity voltage-stabilized active power reference value P SC The calculation formula is as follows: Among them, P SCmax k is the over-capacity charge and discharge active power limit, which is used to limit the over-capacity charge and discharge power value; SC is the excess power ratio coefficient; ΔU SC is the over-capacity voltage deviation value, which is calculated as follows: ΔU SC =U SCavg -U SCref Among them, U SCref is the overcapacity voltage reference value, U SCavg is the average overcapacitance voltage; S202, voltage phase control According to the active power reference value P ref , generating a voltage phase reference value through the voltage phase control law to adjust the output phase of the cascaded super-capacitor energy storage module; S203, voltage amplitude stabilization control The modulation voltage reference value is generated by the dynamic damping voltage control law and the voltage amplitude control law to drive the cascaded super-capacitor energy storage module to stabilize the load voltage amplitude.

2. The method according to claim 1, characterized in that In step S201, the average over-capacity voltage U is calculated by dividing the sum of the over-capacity voltages of each submodule by the total number of submodules. SCavg , as shown in the following formula: Where N is the number of submodules in each phase, j = 1, 2, ..., N; U sc,aj 、U sc,bj 、U sc,cj They are the overcapacity voltage of each submodule in the three phases.

3. The method according to claim 1, characterized in that In step S202, the voltage phase control law is as follows: i ref =(Δω+ω0) / s Among them, θ ref is the voltage phase reference value; s is the Laplace operator; ω0 is the load rated angular frequency; Δω is the angular frequency correction, and its calculation formula is as follows: Where s is the Laplace operator; ω c is the voltage phase control cutoff frequency; m is the voltage phase control proportional coefficient.

4. The method according to claim 1, wherein The step S203 includes two steps: dynamic damping voltage calculation and voltage amplitude control, specifically including: S2031, Dynamic Damping Voltage Calculation The dynamic damping voltage is used to eliminate the oscillation risk caused by transient impact disturbances. The d-axis and q-axis dynamic damping voltages v are calculated according to the dynamic damping voltage control law. zd and v zq , the specific calculation formula is as follows: Where s is the Laplace operator; ω z is the cutoff frequency of dynamic damping control; i d and i q are the d-axis and q-axis output currents respectively; k z is the high-pass filter proportional coefficient; r z is the damping coefficient; S2032, voltage amplitude control The voltage amplitude control law is used to achieve stable control of the load voltage amplitude. The specific calculation formula is as follows: m d =(k pv +k iv / s)(V ref -V m )-v zd m q =-in zq Among them, m d and m q They represent the d-axis and q-axis modulation voltage reference values respectively; s is the Laplace operator, k pv k is the load voltage control proportional coefficient; iv is the load voltage control integral coefficient; V ref is the load voltage amplitude reference; V m is the load voltage amplitude; Then, using the voltage phase reference value θ ref , d-axis modulation voltage reference value m d and q-axis modulation voltage reference value m q Perform inverse coordinate transformation to obtain the three-phase modulation voltage reference value m a ,m b ,m c ; Using m a ,m b ,m c Modulate and drive the cascaded super-capacity energy storage module to operate.

5. A medium voltage uninterruptible power supply system based on cascaded super-capacity energy storage, applying the control method of medium voltage uninterruptible power supply based on cascaded super-capacity energy storage according to any one of claims 1 to 4, characterized in that: The system includes: isolation reactor L i , filter reactor L f , cascade super-capacity energy storage module, load side switch S1, grid side switch S2, bypass switch S3 and controller; the load side switch S1, isolation reactor L i , the grid-side switch S2 is sequentially connected in series between the load and the grid, and is connected in parallel with the bypass switch S3; the cascaded super-capacitor energy storage module is connected through the filter reactor L f Connect to the isolation reactor L i Between the load side switch S1; Among them, the isolation reactor L i Used to limit the fault current during grid faults, cascade super-capacity energy storage modules are used to stabilize the load bus voltage, and filter reactor L f Used to suppress the output harmonics of cascaded super-capacitor energy storage modules; The cascaded supercapacitor energy storage module has a three-phase structure, with each phase consisting of N submodules of the same structure connected in series. Each submodule includes a supercapacitor, a filter capacitor and an H-bridge converter arranged in parallel. The supercapacitor is referred to as a supercapacitor. The number N of submodules in each phase of the cascaded supercapacitor energy storage module and the capacitance value of the supercapacitor in the submodule are configured according to the actual requirements of the power supply power and power supply duration of the medium voltage load.

6. The system according to claim 5, characterized in that According to the commissioning of the cascaded super-capacity energy storage module, the medium-voltage uninterruptible power supply system operates as follows: (1) When the cascaded super-capacity energy storage module is able to operate normally, the medium-voltage uninterruptible power supply system operates in a voltage stabilization mode; in this mode, the load-side switch S1 and the grid-side switch S2 are in a closed state, and the bypass switch S3 is in an open state; by executing the steps to control the operation of the cascaded super-capacity energy storage module, a stable load voltage is achieved; (2) When the cascaded super-capacity energy storage module fails and is removed, the medium-voltage uninterruptible power supply system operates in bypass mode: in this mode, the load-side switch S1 and the grid-side switch S2 are in the open state, the bypass switch S3 is in the closed state, and the load is directly powered by the grid.

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