Uninterruptible power supply system based on network construction type energy storage converter

Abstract

The invention relates to the technical field of power grid power supply, in particular to an uninterruptible power supply system based on a network construction type energy storage converter, which comprises the network construction type energy storage converter, an LC filter, a common connection point PCC and a local load, and is characterized in that the network construction type energy storage converter is connected to the common connection point PCC through the LC filter and is connected with a power grid through the common connection point PCC; meanwhile, a local load is accessed; the control unit comprises an active instruction generation unit, an active frequency control unit, a reactive voltage control unit, a voltage and current double-closed-loop control unit and an SOGI signal generator, and compared with an on-line double-conversion UPS, electric energy only needs to be subjected to one-time inversion energy conversion through the scheme, and the overall efficiency is high. And the reactive voltage loop is adjusted, so that no reactive power transmission exists between the common connection point and the power grid, and the digital control implementation mode is simple.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid power supply, and particularly provides an uninterrupted power supply system based on a network-structured energy storage converter. BACKGROUND

[0002] With the acceleration of global digitalization and intelligentization, electricity has become the blood of social operation. From data centers, cloud computing platforms, industrial automation to financial transactions, medical health and communication networks, the dependence of countless critical devices and systems on electricity has reached an unprecedented level. However, the existing power grid management faces many challenges, such as complete interruption (power failure), voltage sag / rise, frequency fluctuation, harmonic distortion, and transient pulse, surge, etc. These power quality problems may cause data loss, hardware damage, production interruption, service stop, and thus cause huge economic losses. Uninterruptible power supply system (UPS) is a key power guarantee device that emerges in this background, and its core mission is to provide uninterrupted and high-quality power to the load when the power supply is abnormal or interrupted, and to ensure the continuous operation of critical businesses. After decades of development, UPS technology has formed several mainstream topologies, including backup UPS, online interactive UPS and online double-conversion UPS. However, these traditional architectures have inherent and difficult-to-reconcile contradictions between performance, efficiency and cost.

[0003] Backup UPS does not need complex rectifiers and large converters to work continuously, has fewer internal components, low technical requirements, and the lowest manufacturing cost and market price among all UPS types. However, when the power supply is abnormal and switched to battery power, there will be an interruption of 2ms to 10ms. The capacitance stored in the internal power supply of modern computers is enough to support this millisecond interruption, so this switching is usually "insensitive" to hosts, displays and other devices, and the devices will not restart. However, for some extremely precise devices, such as high-end servers, medical instruments, storage devices or some network hardware, this millisecond power failure may cause unexpected device restart, data loss or system error.

[0004] Online interactive UPS has a converter always in parallel with the output, in a "hot standby" state, so its response speed is faster than that of backup UPS when switching to battery mode, and the conversion time can be shortened to 2-4 milliseconds or even shorter. Although the switching time is very short, for critical devices that require absolute zero interruption (such as core servers in top-level data centers), this millisecond interruption may still cause unexpected device restart, data loss or system error.

[0005] The online double conversion UPS is always working for the load, and the disappearance of the mains only means that the source of the DC power is switched from the rectifier to the battery, and this process is an electronic level switching without mechanical action, and zero millisecond interruption can be realized. However, due to the large number of components, the price is higher than that of other types of UPS, and due to the fact that the electrical energy needs to be converted twice through rectification and inversion, energy is lost in the form of heat during each conversion, so the overall efficiency is relatively low, which means higher electricity charges, and additional air conditioning cooling costs are needed to eliminate the heat, which is a huge ongoing operating cost.

[0006] In actual application scenarios, there is a typical hybrid power supply working condition: a network-capable converter is connected to both local loads and the public power grid. In this system, an ideal and efficient energy management goal is to preferentially use the electrical energy output by the converter (usually connected to an energy storage system and a new energy source) to supply the local load, minimize the power taken from the power grid, thereby reducing the user's electricity cost, and achieving local energy consumption. When the load power exceeds the rated capacity threshold of the converter, the system needs to switch between different operating modes (for example, from all converter power supply to converter and grid combined power supply). If the strategy is not properly designed, it will cause a large transient impact on voltage and current at the moment of mode switching, which threatens the safe and stable operation of the converter itself and the load equipment.

[0007] Currently, there is a lack of control strategy design for this working condition in the industry, and there is an urgent need for a load uninterrupted power supply system with simple control structure, rapid dynamic response, high overall efficiency and seamless mode switching. SUMMARY

[0008] In order to overcome the above defects, the present application is proposed to provide a solution to the technical problems of low response and high cost in the control of existing uninterruptible power supply systems.

[0009] The present application provides an uninterrupted power supply system based on a network-capable energy storage converter, comprising a network-capable energy storage converter, an LC filter, a public connection point PCC and a local load, wherein the network-capable energy storage converter is connected to the public connection point PCC through the LC filter, and is connected to the power grid through the public connection point PCC and the local load. Further, it further comprises a control unit, wherein the control unit comprises active instruction generation, active frequency control, reactive voltage control, voltage and current double closed loop control and SOGI-based power calculation, The SOGI-based power calculation is used to calculate the converter output power, the grid output active power and the grid output reactive power according to the collected filter capacitor voltage signal, filter capacitor current signal and grid side current signal. Active command generation is used to generate the active power command of the converter according to the grid active power command and the converter output power through a first PI controller; Active frequency control is used to generate the angular frequency and phase according to the converter active power command and the converter output power by using the principle of virtual synchronous machine; Reactive voltage control is used to generate the given amplitude of the voltage through a second PI controller according to the grid reactive power command and the grid output reactive power; The voltage and current double closed loop control link is used to generate the modulation signal and control the switch of the converter using the modulation signal.

[0010] Further, the control unit is configured to perform the following steps: Collecting the filter capacitor voltage signal v C , the filter capacitor current signal i o and the grid side current signal i g ; Filtering the collected signals and constructing virtual quadrature components to obtain two-way quadrature output signals of each collected signal α channel and β channel; Based on the two-way quadrature output signals of each collected signal α channel and β channel, the converter output power , the grid output active power , and the grid output reactive power are calculated; The converter active power command is calculated through the first PI controller, wherein, is the grid active power command, is the proportional coefficient of the first PI controller, is the integral element; The angular frequency is calculated according to the formula by using the principle of virtual synchronous machine, and the phase is obtained after integration, wherein, is the rated angular frequency, which is set to 100Π rad / s, J is the virtual moment of inertia, and D is the virtual damping coefficient; The output is calculated through the second PI controller, wherein, is the grid reactive power command, is the proportional coefficient of the second PI controller, is the integral element; Based on the phase and the given amplitude of the voltage , the output voltage given value is synthesized; The inductance current given value is calculated through the voltage loop controller, wherein, is a proportional coefficient of the voltage loop controller, is a resonance coefficient, is a cut-off bandwidth, is a resonance frequency, set to 100Π rad / s; is calculated according to the deviation of the inductor current given value and the filter capacitor current signal i o , , is a proportional coefficient of the current loop controller.

[0011] Further, the grid active instruction is set to 0, and the grid reactive instruction is set to 0.

[0012] Further, the filtering and constructing virtual orthogonal components of the collected signals include: respectively, the filter capacitor voltage signal v C , the filter capacitor current signal i o and the grid side current signal i g are substituted into the transfer function , , to calculate two-way orthogonal output signals corresponding to each input signal, wherein, is an input signal, and are two-way orthogonal output signals through the SOGI signal generator, s is the Laplace operator, is an angular frequency, and k is a SOGI parameter.

[0013] Further, the parameter k of the SOGI is 1.414.

[0014] Further, based on the two-way orthogonal output signals of each collected signal α channel and β channel, the converter output power , the grid output active power , and the grid output reactive power are calculated, including: the two-way orthogonal output signals corresponding to the filter capacitor voltage signal v C and the two-way orthogonal output signals corresponding to the filter capacitor current signal i o are substituted into , to calculate the converter output power ; the two-way orthogonal output signals corresponding to the filter capacitor voltage signal v C and the two-way orthogonal output signals corresponding to the grid side current signal i g are substituted into , the grid output active power ; the filtered capacitor voltage signal v C corresponding two-way orthogonal output signal and grid side current signal i g corresponding two-way orthogonal output signal into , the grid output reactive power ; wherein, and are the corresponding two-way orthogonal output signals of the voltage signal, and are the corresponding two-way orthogonal output signals of the current signal.

[0015] Further, the voltage loop controller adopts a proportional-resonant controller.

[0016] Further, the current loop controller adopts a proportional controller.

[0017] Working principle and beneficial effects of the present application: In the implementation of the technical solutions of the present application, the grid-connected energy storage converter preferentially outputs electrical energy to supply the local load, maximally reduces the power taken from the grid, thereby reducing the user's electricity cost and realizing the on-site consumption of energy. The converter can operate in both overload and non-overload conditions, and the switching between the two conditions does not affect the stability of the system.

[0018] Compared with the backup UPS and the online interactive UPS, there is no power outage time, and the efficient energy management goal can be achieved. Even if the power grid is suddenly powered off, the grid-connected energy storage converter can continue to supply power to the local load, and the normal operation of the precision equipment is not affected. Compared with the online double-conversion UPS, the electrical energy only needs to be converted once through inversion, and the overall efficiency is high, thereby filling the vacancy of the control technology in this working condition. Moreover, the present application only needs to increase an active instruction generation before the active frequency control and adjust the reactive voltage loop so that there is no reactive power transmission between the point of common coupling and the grid, and the digital control implementation is simple. BRIEF DESCRIPTION OF DRAWINGS

[0019] The disclosed content of the present application will become more easily understood with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes, and are not intended to limit the scope of protection of the present application. In addition, similar numbers in the drawings are used to represent similar components, wherein: Figure 1is a structural schematic diagram of an uninterrupted power supply system based on a grid-forming energy storage converter according to the present application; Figure 2 is a circuit topology schematic diagram of a control unit in the present application; Figure 3 is an active power waveform diagram of the converter and the grid in the uninterrupted power supply system according to the present application; Figure 4 is a reactive power waveform diagram of the converter and the grid in the uninterrupted power supply system according to the present application. DETAILED DESCRIPTION

[0020] Some embodiments of the present application will be described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present application, and are not intended to limit the protection scope of the present application.

[0021] Figure 1 is a structural schematic diagram of an uninterrupted power supply system based on a grid-forming energy storage converter according to the present application. As shown in Figure 1 the uninterrupted power supply system based on a grid-forming energy storage converter in the present embodiment includes a control unit, a grid-forming energy storage converter, an LC filter composed of a filter inductance Lf and a filter capacitance Cf, a point of common coupling (PCC), a grid equivalent inductance Lg, and a local load. The grid-forming energy storage converter is connected to the point of common coupling PCC through the LC filter, and is connected to the grid through the point of common coupling PCC, while being connected to the local load.

[0022] The control unit includes active instruction generation, active frequency control (virtual synchronous machine control), reactive voltage control, voltage and current double closed loop control, and SOGI-based power calculation. Among them: a. The active instruction generation link is used to generate the active power instruction of the converter according to the relationship between the load power and the rated power of the converter, specifically: a1, the filter capacitance voltage signal and the output current signal on the output side of the converter, and the grid side current signal are collected; a2, the above signals are filtered and virtual quadrature components are constructed; a3, the converter output active power and the grid output active power are calculated; a4, the active power instruction of the converter is generated through a PI controller, wherein the grid active instruction is set to zero.

[0023] b. The active frequency control link is based on virtual synchronous machine control to generate output voltage frequency and phase information.

[0024] c. The reactive voltage control link makes the grid reactive power follow the instruction value without error through a PI controller, and the sum of the output value of the PI controller and the rated voltage is used as the amplitude of the given value of the converter output voltage.

[0025] d. The voltage and current dual closed-loop control loop is used to synthesize the output voltage setpoint and generate the modulation signal. Specifically, the voltage loop is used to obtain the inductor current setpoint, the current loop uses a proportional controller, and the output is used to generate the converter's modulation signal after a delay.

[0026] e. SOGI-based power calculation is used to calculate the converter output power, grid output active power, and grid output reactive power based on the collected filter capacitor voltage signal, filter capacitor current signal, and grid-side current signal.

[0027] Specifically, when the load power is less than the converter's rated power, all power is provided by the converter, and the power grid does not provide any power; when the load power is greater than the converter's rated power, the converter provides its rated power, and the remaining power is provided by the power grid.

[0028] In one implementation, Figure 2 This is a schematic diagram of the circuit topology of the control unit in this invention. The control unit is configured to perform the following steps S1-S6.

[0029] S1: Acquire the voltage signal v of the filter capacitor on the output side of the converter. C , filter capacitor current signal i o and grid-side current signal i g ; S2: In SOGI-based power calculation, an SOGI (Second-Order Generalized Integrator) signal generator is used to filter the acquired signal and construct virtual orthogonal components, which are then processed through a transfer function. , The two orthogonal output signals of the α channel and β channel are calculated, where, For input signal, and These are the two orthogonal output signals from the SOGI signal generator, where s is the Laplace operator. ω is the angular frequency (obtained from the active frequency control), k is the SOGI parameter, and considering the trade-off between response speed and oscillation, k is usually chosen as 1.414; Specifically, the voltage signal v of the filter capacitor is respectively... C , filter capacitor current signal i o and grid-side current signal i g Substitute the input signal into the transfer function , The two orthogonal output signals corresponding to each input signal are calculated.

[0030] pass and Calculate the converter output power grid output active power grid output reactive power wherein, and are two quadrature output signals corresponding to the voltage signal, and are two quadrature output signals corresponding to the current signal.

[0031] Specifically, the filtered capacitor voltage signal v C corresponding two quadrature output signals and the filtered capacitor current signal i o corresponding two quadrature output signals are substituted into to calculate the converter output power , the filtered capacitor voltage signal v C corresponding two quadrature output signals and the grid side current signal i g corresponding two quadrature output signals are substituted into to calculate the grid output active power , the filtered capacitor voltage signal v C corresponding two quadrature output signals and the grid side current signal i g corresponding two quadrature output signals are substituted into to calculate the grid output reactive power .

[0032] S3: In active instruction generation, based on the grid output active power , the converter active power instruction is calculated via the first PI controller, wherein, is the grid active instruction, set to 0, is the proportional coefficient of the first PI controller, is the integral element, and the upper limit of the amplitude limiting output by the first PI controller is set to the rated power, i.e. the maximum active instruction is the rated power.

[0033] S4: In active frequency control, based on the converter active power instruction , the converter output power , the angular frequency is calculated according to the formula using the principle of virtual synchronous machine, and the phase is obtained after integration, wherein, is the rated angular frequency, set to 100Π rad / s, J is the virtual moment of inertia, and D is the virtual damping coefficient.

[0034] S5: In reactive voltage control, based on the grid output reactive power the deviation of the instruction value Qgref of the voltage loop QPR controller from zero wherein, is the grid reactive power instruction, set to 0, is the proportional coefficient of the second PI controller, is the integral term.

[0035] S6: In the voltage and current double-loop control, based on the phase and the given amplitude of the voltage , the output voltage given value is synthesized; Through the voltage loop QPR controller, the inductor current given value is calculated according to the deviation of the output voltage given value C from the filtered capacitor voltage signal v , wherein, is the proportional coefficient of the QPR controller, is the resonance coefficient, is the cutoff bandwidth, is the resonance frequency, set to 100Π rad / s; Through the current loop P controller and the delay link, the modulation signal is calculated according to the deviation of the inductor current given value o from the filtered capacitor current signal i , is the proportional coefficient of the P controller.

[0036] In actual engineering, the current loop output generates the modulation signal of the converter after a one-beat delay caused by calculation and loading.

[0037] Based on the above steps S1-S6, the system makes the load power less than the rated power of the converter, and the power is provided by the converter, and the grid does not provide any power. When the load power is greater than the rated power of the converter, the converter provides the rated power, and the remaining power is provided by the grid. The technology mainly includes the following aspects.

[0038] An active power command generation stage is added before the active power frequency loop. This stage generates the active power command value for the converter output. Under no-load conditions, the grid does not output active power; therefore, the given grid active power command is zero. A PI controller is used to ensure the grid active power tracks the command value without error, and the controller's output value is the converter's active power command. The feedback power of the active power command generation stage is the active power absorbed by the grid. When this power is greater than zero, it indicates that the converter is simultaneously outputting active power to both the load and the grid. The converter's active power command value needs to be reduced, thereby reducing the angle between the point of common coupling voltage and the grid voltage (i.e., the power angle), and reducing the active power transmitted to the grid until it reaches zero. When this power is less than zero, it indicates that the grid is outputting active power to the point of common coupling. The converter's active power command value needs to be increased, thereby increasing the power angle and reducing the active power transmitted from the grid to the point of common coupling until it reaches zero. Under overload conditions, the converter needs to output its rated power, and the grid also outputs active power. The error between the active power command generation loop command and the feedback quantity is greater than zero. The active power command of the converter is continuously increased through the PI controller, and the controller output is limited so that the active power command increases to its rated power.

[0039] The reactive voltage loop is used to control the power grid to not output reactive power. Given that the reactive power command of the power grid is zero, a PI controller is used to make the reactive power of the power grid track the command value without error. The sum of the controller's output value and the rated voltage is used as the amplitude of the converter's output voltage setpoint.

[0040] It should be noted that although the steps in the above embodiments are described in a specific order, those skilled in the art will understand that in order to achieve the effects of the present invention, different steps do not necessarily have to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders, and these variations are all within the scope of protection of the present invention.

[0041] Example 2 A simulation is performed using a single-phase grid-type energy storage converter with a rated power of 5kW as an example. Figure 3 This is a waveform diagram of the active power of the converter and the power grid in the uninterruptible power supply system of this invention. Figure 4 This is a waveform diagram of the reactive power of the converter and the power grid in the uninterruptible power supply system of this invention. For example... Figures 3-4 The simulation results are shown in the figure.

[0042] Before 1.5 seconds, the load was not overloaded, and the grid output active power. The value is approximately 0, meaning the entire load power is supplied by the converter.

[0043] At 1.5s, the load power suddenly increased to over 5kW, indicating that the converter's output power... Maintaining the rated value of 5kW, the excess power will be supplied by the grid. >0).

[0044] At 2.5s, the load power recovers to below the rated value. After a transient process, the system returns to the state where it is independently powered by the converter. Restored to 0).

[0045] Throughout the process, the power grid outputs reactive power. The system consistently maintains a value near 0, and remains stable during the switching between the two operating conditions.

[0046] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. An uninterruptible power supply system based on a grid-type energy storage converter, comprising a grid-type energy storage converter, an LC filter, a point of common coupling (PCC), and a local load, wherein the grid-type energy storage converter is connected to the PCC through the LC filter and is connected to the power grid through the PCC, and is also connected to the local load; Its features are, It also includes a control unit, which comprises active power command generation, active power frequency control, reactive power voltage control, voltage and current dual closed-loop control, and SOGI-based power calculation. SOGI-based power calculation is used to calculate the converter output power, grid output active power, and grid output reactive power based on the collected filter capacitor voltage signal, filter capacitor current signal, and grid-side current signal. The active power command generation is used to generate the active power command of the converter through the first PI controller based on the active power command of the power grid and the output power of the converter. Active frequency control is used to generate angular frequency and phase based on the converter's active power command and converter output power, using the principle of a virtual synchronous machine. Reactive voltage control is used to generate a given voltage amplitude through a second PI controller based on the grid reactive power command and the grid output reactive power. The voltage and current dual closed-loop control circuit is used to generate a modulation signal and use the modulation signal to control the switching of the converter.

2. The uninterruptible power supply system based on a grid-type energy storage converter according to claim 1, characterized in that, The control unit is configured to perform the following steps: Acquire the voltage signal v of the filter capacitor on the output side of the converter. C , filter capacitor current signal i o and grid-side current signal i g ; The acquired signals are filtered and virtual quadrature components are constructed to obtain two quadrature output signals, α channel and β channel, for each acquired signal. Based on the two quadrature output signals of each acquired signal's α and β channels, the converter's output power is calculated. Active power output of the power grid Reactive power output from the power grid ; The active power command of the converter is calculated by the first PI controller. ,in, For active power commands of the power grid, The proportional gain of the first PI controller. This is a points-based system; The angular frequency is calculated using the principle of a virtual synchronizer and the formula. The phase is obtained after integration. ,in, The rated angular frequency is set to 100π rad / s, J is the virtual moment of inertia, and D is the virtual damping coefficient. The output is calculated by the second PI controller. ,in, For reactive power command of the power grid, The proportional gain of the second PI controller. This is a points-based system; Based on phase and the given amplitude of voltage Synthetic output voltage setpoint ; The inductor current setpoint is calculated using a voltage loop controller. ,in, This is the proportional gain of the voltage loop controller. The resonance coefficient, For cutoff bandwidth, The resonant frequency is set to 100 π rad / s; The current loop controller and delay circuit are used to determine the inductor current setpoint. With the filter capacitor current signal i o The deviation is used to calculate the modulated signal. , This is the proportional gain of the current loop controller.

3. The uninterruptible power supply system based on a grid-type energy storage converter according to claim 2, characterized in that, The power grid active power command Setting it to 0, the power grid reactive power command Set to 0.

4. The uninterruptible power supply system based on a grid-type energy storage converter according to claim 2, characterized in that, The process of filtering the acquired signal and constructing virtual orthogonal components includes: The voltage signal v of the filter capacitor is respectively C , filter capacitor current signal i o and grid-side current signal i g Substitute the input signal into the transfer function , The two quadrature output signals corresponding to each input signal are calculated. in, For input signal, and These are the two orthogonal output signals from the SOGI signal generator, where s is the Laplace operator. ω is the angular frequency, and k is the SOGI parameter.

5. The uninterruptible power supply system based on a grid-type energy storage converter according to claim 4, characterized in that, The parameter k of SOGI is set to 1.

414.

6. The uninterruptible power supply system based on a grid-type energy storage converter according to claim 2, characterized in that, The converter output power is calculated based on the two orthogonal output signals of each acquired signal channel α and β. Active power output of the power grid Reactive power output from the power grid ,include: The filter capacitor voltage signal v C The corresponding two quadrature output signals and filter capacitor current signal i o Substitute the corresponding two quadrature output signals The converter output power was calculated. ; The filter capacitor voltage signal v C The corresponding two quadrature output signals and the grid-side current signal i g Substitute the corresponding two quadrature output signals The active power output of the power grid was calculated. ; The filter capacitor voltage signal v C The corresponding two quadrature output signals and the grid-side current signal i g Substitute the corresponding two quadrature output signals The reactive power output of the power grid was calculated. ; in, and These are two quadrature output signals corresponding to the voltage signal. and These are the two quadrature output signals corresponding to the current signal.

7. The uninterruptible power supply system based on a grid-type energy storage converter according to claim 2, characterized in that, The voltage loop controller is a quasi-proportional resonant controller.

8. The uninterruptible power supply system based on a grid-type energy storage converter according to claim 2, characterized in that, The current loop controller is a proportional controller.

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