NL2021570B1 - Method and system for hierarchically controlling cascaded rectifiers - Google Patents

Method and system for hierarchically controlling cascaded rectifiers Download PDF

Info

Publication number
NL2021570B1
NL2021570B1 NL2021570A NL2021570A NL2021570B1 NL 2021570 B1 NL2021570 B1 NL 2021570B1 NL 2021570 A NL2021570 A NL 2021570A NL 2021570 A NL2021570 A NL 2021570A NL 2021570 B1 NL2021570 B1 NL 2021570B1
Authority
NL
Netherlands
Prior art keywords
voltage
sub
module
initialization
modulation signal
Prior art date
Application number
NL2021570A
Other languages
Dutch (nl)
Inventor
Sun Yao
Hou Xiaocao
Su Mei
Han Hua
Wang Hui
Liu Yonglu
Xiong Wenjing
Original Assignee
Univ Central South
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Univ Central South filed Critical Univ Central South
Application granted granted Critical
Publication of NL2021570B1 publication Critical patent/NL2021570B1/en

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/25—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only arranged for operation in series, e.g. for multiplication of voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/0074—Plural converter units whose inputs are connected in series

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Rectifiers (AREA)

Abstract

The present disclosure provides a method for hierarchically controlling cascaded rectifiers, comprising steps of: generating an initialization parameter set in an upper controller for starting up the cascaded rectifiers; transmitting the initialization parameter to multiple lower controllers via communication link by the upper controller, wherein each lower controller is configured to connect with and control a corresponding one of sub-modules of the cascaded rectifiers, lower controllers generates PWM initialization modulation signal based on the initialization parameter set, and send the PWM initialization modulation signal as a command to each module in real time so as to start up the cascaded rectifiers, in the meantime gathering voltage and current to a front-end input and from a back-end output of the sub-modules after started, generates a PWM real-time modulation signal based on further calculation on the gathered voltage and current value, and control a voltage input to the sub-module correspondingly connected thereto by the PWM real-time modulation signal.

Description

METHOD AND SYSTEM FOR HIERARCHICALLY CONTROLLING
CASCADED RECTIFIERS
Technical Field
The present disclosure relates to power electronic control system, particularly to a method and a system for hierarchically controlling cascaded rectifiers, which applies in the fields of energy internet, high voltage power distribution network, electrical railway traction.
Technical Background
Cascaded rectifiers, as rectifying part of a front end of power electronics transformer and energy router, are widely applied in occasions of electrical railway traction and energy internet, and are the main device for existing Medium/High voltage energy conversion. In comparison with typical neutral point clamped multi-level converter, the cascaded rectifiers have advantages of independent sub-module, being easily extended, and simple structure etc.
For the cascaded rectifiers of the Medium/High voltage power system, it is essential to implement cooperative controlling among the submodules. With respect to the existing study, all the control goals are fulfilled in the centralized structure. In this case, a centralized controller is needed to gather global information such as signals of output voltage and current, voltage across the capacitor placed in the DC side of all modules, and voltage across the grid side, and process and provide given reference signals, so as to implement balanced voltage across the capacitors of all the modules, balanced reactive compensation between the modules, and synchronized frequency with the grid voltage. Since the signals transmitted therefrom are alternative and periodical, it is necessary to adopt high band-width communication during signal transmission.
In addition, since the global infonnation for being gathered is considerably enormous, especially in the case of a large number of cascaded modules of extreme high-voltage power system, the centralized controller with powerful processing capability is needed. In the meantime, one single centralized controller manages all the modules, and thus packet loss or delay taking place in one single module will easily incur communication failure of the whole cascaded rectifiers. Therefore, the reliability of the whole system will be significantly influenced due to the failure in the single module.
To overcome the above drawbacks, such as lowering requirements for communication bandwidth of cascaded rectifiers and processing capability of the central controller, and enhancing communication reliability of the whole system, a novel control staicture is needed, so that the application scale of the cascaded rectifiers is expanded and thus the application cost can be further reduced.
Summary of the Invention
To solve the above technical problems, the present disclosure provides a method for hierarchically controlling cascaded rectifiers, comprising steps of: generating an initialization parameter set in an upper controller for starting up the cascaded rectifiers; transmitting, by the upper controller, the initialization parameter to multiple lower controllers via communication link, wherein each lower controller is configured to connect with and control a corresponding one of sub-modules of the cascaded rectifiers; generating, in each lower controller, PWM initialization modulation signal based on the initialization parameter set received, and sending the PWM initialization modulation signal as a command to each sub-module in real time so as to start up the cascaded rectifiers, and in the meantime gathering voltage and current to a front-end input and from a back-end output of the sub-modules after started; obtaining, in each lower controller, a PWM real-time modulation signal based on further calculation on values of the voltage and current gathered in real time, and controlling a voltage input to the sub-module correspondingly connected thereto by the PWM real-time modulation signal; automatically detaching a connection of one of the sub-modules with the system, once detecting abnormal voltage or current value in said one of the sub-modules by the lower controller, and reporting a message of failure to the upper controller; and receiving, by the upper controller, the message of failure, regenerating an initialization parameter set and transmitting it to each lower controller so as to reallocate the voltage input to each of remaining sub-modules in the cascaded rectifiers from the power grid.
According to one embodiment of the disclosure, it is preferred that the initialization parameter set comprises an initialization voltage value, an initialization phase angle and a nominal active power reference.
According to one embodiment of the disclosure, the step of generating initialization parameter set in an upper controller for starting up the cascaded rectifiers, further comprises sub-steps of: generating the initialization voltage value and the initialization phase angle based on an amplitude value and a phase angle of a voltage detected from the power grid; obtaining a nominal active power reference based on load requirements. According to one embodiment of the disclosure, the step of obtaining PWM real-time modulation signal further comprises sub-steps of: calculating a current active power of the sub-module based on the voltage and current detected on the front-end input, so as to determine a phase angle reference of an input voltage; determining an amplitude reference of the input voltage based on power factor index of the grid-connected; composing the phase angle reference and the amplitude reference into a voltage reference input to the sub-module from the power grid; and obtaining a PWM real-time modulation signal to be sent from the lower controller to the rectifier sub-modules based on the voltage reference.
According to a method for hierarchically controlling cascaded rectifiers in the disclosure, it is preferred that the step of determining an amplitude reference of the input voltage based on power factor index of the grid-connected further comprises, obtaining an amplitude of the voltage input to the sub-module to be controlled based on the following equation:
in starting-up state,
in operating state,
wherein, V, represents the amplitude reference of the voltage input to rectifier sub-module /', Vo represents the initialization voltage value provided by the upper controller, with different values in starting-up state and operating state, and can be set a value based on adjustable grid-connected power factor in operating state, Vg represents the amplitude of the real-time voltage across the power grid, Vg* represents the amplitude of the nominal voltage of the power grid, Nfew represents the number of modules taking part in compensation for fluctuation of the voltage across the grid, in general Njew~ 10%N~20%N, N represents the number of cascaded rectifier sub-modules, and δ is a difference of the phase angle between the cascaded rectifiers and the power grid in steady state.
According to a method for hierarchically controlling cascaded rectifiers in the disclosure, in the step of calculating the current reactive power output of the sub-module based on the voltage and current input to the front end of the sub-module gathered, so as to determine the phase angle reference of the input voltage, the phase angle reference and frequency of the voltage input to the sub-module to be controlled are obtained based on the following equation:
wherein, co, represents the angular frequency reference of the voltage input to rectifier sub-module /, co* represents a nominal angular frequency of the power grid, kp is a positive gain, P* represents input active power reference, and in general Pi* is determined based on a power of the load, and to ensure a balance of a voltage on DC capacitor of the load side, P,* is designed as:
wherein Vda represents a voltage on capacitor of the load side of rectifier sub-module i, V*dc represents a nominal voltage reference of the capacitor, Po represents a nominal
active power reference, kp and fo are respectively proportional-integral coefficients, and s is Laplace operator.
In one embodiment of the disclosure, it is preferred that impedance of the connection between each submodule of the cascaded rectifiers and the power grid can be modified to be of inductance characteristic through adding a virtual inductor or placing a real inductor therein, and thus the input power transmission characteristic of the grid-connected with resistance characteristic can be represented as follows:
wherein P, and Q, respectively represent the input active power and input reactive power of rectifier sub-module Ï, fZ/ine I represents impedance modulus of the grid-connected, and Vg and respectively represent the amplitude value and the phase angle of the voltage across the power grid.
According to another aspect of the present disclosure, a system for hierarchically controlling cascaded rectifiers is provided, which comprises: an upper controller, for generating an initialization parameter set and transmitting the initialization parameter set via communication link so as to start up the cascaded rectifiers, multiple lower controllers, being communicatively connected to the upper controller and correspondingly connected with a corresponding one of sub-modules of the cascaded rectifiers via hard wires, each lower controller being used for: generating a PWM initialization modulation signal based on the initialization parameter set received and sending the PWM initialization modulation signal as a command to each sub-module in real time so as to start up the cascaded rectifiers, and in the meantime gathering a voltage and current input/output from or to a front end/back end of each sub-modules after started; obtaining a PWM real-time modulation signal based on further calculation on the voltage and current gathered in real time, and controlling a voltage input to the sub-module being correspondingly connected thereto by the
PWM real-time modulation signal; and automatically detaching a connection of one of the sub-modules with the system, once detecting abnormal voltage or current in said one of the sub-modules, and reporting a message of failure to the upper controller; wherein the upper controller further includes a failure processing unit for receiving the message of failure, regenerating an initialization parameter set and transmitting it to each of multiple lower controller so as to reallocate the voltage input to each of remaining sub-modules in the cascaded rectifiers.
According to the system for hierarchically controlling the cascaded rectifiers, the lower controller includes. an active power frequency controlling unit, for calculating a current active power of the sub-module based on voltage and current of the front-end input of the sub-module, so as to determine a phase angle reference of input voltage; a reactive power voltage controlling unit, for determine an amplitude reference of the input voltage based on power factor index of the grid-connected a synthesis unit, for composing the phase angle reference and the amplitude reference into a voltage reference input to the sub-module; PWM modulation signal output unit, for obtaining a PWM real-time modulation signal to be sent from the lower controller based on the voltage reference.
To solve problems in centralized control framework of cascaded rectifiers, the present disclosure provides a hierarchical control framework based on multiple time scales, wherein the upper ancillary controller is in charge of services like starting up of the whole system, power allocation and failure management etc., so that single sub-module controlled by the corresponding lower controller can enable autonomous balancing of voltage across the DC capacitor and autonomous synchronization of the power grid frequency. Advantages of the present disclosure are generally as follows, 1) the designed hierarchical control can decouple different controls from each other based their different time scales, wherein the upper controller is designed for provide the ancillary services in slow time scale, and the lower controller is designed for controlling of single sub-module in fast time scale, and thus the hierarchy of the control is clear and can be easily implemented. 2) the control method provided herein can achieve autonomous balancing of the voltage on the capacitor and autonomous synchronization of frequency of the power grid without schedule from a central controller; 3) both the physical structure of the cascaded rectifiers and the lower controller are designed in modules and thus can be flexibly extended; 4) the hierarchical control method presented herein significantly reduces the communication traffic between the upper controller and the lower controllers and thus improves the reliability of the system and reduces the cost of the communication of the system; 5) the hierarchical control method presented herein enable to promote wide application of the cascaded rectifiers in extreme high/high voltage power system.
Other features and advantages of the present disclosure will be further explained in the following description, and will partly become self-evident therefrom, or be understood through the implementation of the present disclosure. The objectives and advantages of the present disclosure will be achieved through the structures specifically pointed out in the description, claims, and the accompanying drawings.
Brief Description of the Drawings
The accompanying drawings, together with the embodiments, are provided for a further understanding of the present disclosure, and constitute a part of the description, and are not intended to limit the present disclosure, wherein
Fig. 1 shows a structure block diagram of cascaded rectifiers according to one embodiment of the present disclosure;
Fig. 2 shows an internal staicture block diagram of one sub-module in the cascaded rectifiers;
Fig. 3 shows waves of the grid-connected current, input alternative voltage, and a voltage on the DC capacitor at load side, an operating frequency of sub-module i and transmission power; and
Fig. 4 shows waves of active power and reactive power input to the four sub-modules.
Detailed Description of the Embodiments
The present disclosure will be explained in detail below with reference to the accompanying drawings, so that the objective, technical solutions and advantages thereof can be understood more clearly. It should be noted that each embodiment and feature thereof can be combined each other if there is no conflict, and the technical solutions formed thereby are all fallen in the scope of the present disclosure.
As shown in Fig. 1, a hierarchical control staicture block diagram of cascaded rectifiers according to one embodiment of the present disclosure is presented.
The upper controller is connected to each of multiple lower controllers via communication link. Each lower controller is correspondingly connected with each module in cascaded rectifiers via hard wires. The voltage input of each sub-module is controlled by the lower controller correspondingly connected therewith. Then, the upper controller sends a start-up command to combine the whole cascaded rectifier system into the power grid.
As described above, the control system of the present disclosure is divided into two layers from time scale of response control, one is a layer with slow time scale, and the other is a layer with fast time scale. There is a low band-width communication between the upper controller with slow time scale and the lower controller with fast time scale. The content of the low band-width communication is mostly that the upper controller sends a startup command for the system to the lower controller, and the lower controller reports a message of failure to the upper controller when detecting a failure in the rectifiers sub-module being correspondingly connected therewith. In this way, the upper controller is in charge of services like starting up of the whole system, power compensation and failure management etc., and the lower controllers respectively and independently control each module being connected therewith so that single sub-module controlled by the corresponding lower controller can enable autonomous balancing of voltage across the DC capacitor, autonomous synchronization of the power grid frequency, and given active power output.
In particular, the upper controller generates initialization parameter set for starting up the cascaded rectifiers based on calculation and load requirement allocation. The initialization parameter set comprises initialization voltage value, initialization phase angle and active power for supply to the load. The upper controller generates initialization phase angle δο and initialization voltage value Vo for starting up the rectifiers based on information of amplitude and phase angle of the voltage of the power grid obtained by a phase locked loop, so as to achieve a grid connection with no impact of the cascaded rectifiers. Active power reference O* to be supplied to the load can be obtained by the load requirements.
Then, the initialization parameter set as mentioned above can be transmitted to each lower controller via the communication links between the upper controller and each lower controller.
Multiple lower controllers generate PWM initialization modulation signal based on the received initialization parameter set and send the PWM initialization modulation signal as a command to each submodule in real time which is correspondingly connected therewith so as to start up the cascaded rectifiers. Meanwhile, the lower controllers gather voltage and current output from the sub-modules after started, generate a PWM real-time modulation signal based on further calculation on the gathered voltage and current value, and control voltage input to the sub-module being correspondingly connected therewith by means of the PWM real-time modulation signal.
To ensure synchronization of the input voltage, the lower controller of the present disclosure immediately gathers the voltage on the DC capacitor of the back end of rectifier sub-modules to calculate the control, which is totally different from the prior art.
When the lower controllers detect abnormal voltage or current value in the sub-modules, they can automatically detach the connection of one of the modules with the system and make the sub-module with failure in short circuit through a bypass switch, and then report a message of failure to the upper controller via the communication link.
The upper controller receives the reported failure message, and regenerates an initialization parameter set and transmitting it to each of multiple lower controllers via the communication link so as to reallocate the voltage input to each of remaining sub-modules in the cascaded rectifiers.
The reallocated initialization voltage value Vo can be calculated as the following equation:
wherein N represents the total number of rectifiers modules, Νηο>· represents the number of rectifier sub-modules in normal working state, and V* represents amplitude of input voltage of single sub-module in nominal state obtained by steady-state analysis.
In the case of failure, only the amplitude of the voltage to be reallocated needs to be recalculated by the upper controller, rather than the initialization phase angle and active power to be supplied to the load.
As shown in Fig. 2, the internal structure of the lower controller i being connected with the sub-module i is presented. In the figure, the lower controller i further includes an active power frequency controlling unit, a reactive power voltage controlling unit, a synthesis unit and PWM modulation signal output unit. The active power frequency controlling unit is used for calculating the current active power of the sub-module based on the voltage and current from the back-end output, so as to determine the phase angle reference of the input voltage.
In Fig. 2, active power real output Qt of submodules can be calculated by an active power calculation unit. By taking nominal active power reference Q* and active power real input Qj and nominal angular frequency ω* as input, the angular frequency reference ω, of the input voltage to be used to control can be calculated.
Then the phase angle reference can be obtained by transforming the angular frequency reference «>,.
In particular, the angular frequency reference to, of the input voltage and input frequency is obtained based on the following equation:
wherein, to,· represents the angular frequency reference of the voltage input to rectifier sub-module /, to* represents a nominal angular frequency of the power grid, kP is a positive gain, P* represents input active power reference, and in general P* is determined based on a power of the load, and to ensure a balance of a voltage on DC capacitor of the load side, Pi* is designed as:
wherein Vda represents a voltage on capacitor of the load side of rectifier sub-module i, V*dc represents a nominal voltage reference of the capacitor, Po represents a nominal active power reference, kp and ki are respectively proportional-integral coefficients, and s is Laplace operator.
Additionally, as shown in Fig.2, the reactive power voltage unit determines the amplitude reference V, of the voltage input to the sub-module to be controlled based on power factor index of the grid-connected :
in starting-up state,
in operating state,
wherein, V, represents the amplitude reference of the voltage input to rectifier sub-module /, Vo represents the initialization voltage value provided by the upper controller, with different values in starting-up state and operating state, and can be set a value based on adjustable grid-connected power factor in operating state, Vg represents the amplitude of the real-time voltage across the power grid, Vg* represents the amplitude of the nominal voltage of the power grid, Nfew represents the number of
modules taking part in compensation for fluctuation of the voltage across the grid, in general Njeii~ 10%N~2Q%N, N represents the number of cascaded rectifier sub-modules, and δ is a difference of the phase angle between the cascaded rectifiers and the power grid in steady state.
As shown in Fig.2, the calculated amplitude reference and angular frequency reference of the input voltage are transmitted to synthesis unit (not shown), and then the synthesis unit composes the phase reference and the amplitude reference into a voltage reference value input to the sub-module to be correspondingly controlled.
Since output characteristic of each sub-module is no longer a typical current supply, but a voltage supply, the frequency of the output voltage can be automatically synchronized with the power grid, and there is no need to gather the frequency of the power grid in real time and thus significantly reduces the communication traffic of the controllers. In addition, since the voltage input to a single rectifier sub-module can be controlled based on the voltage on the capacitor of the sub-module in the present disclosure, and balance between active power loss and reactive power loss of the sub-module is maintained reasonably, autonomous balance of the voltage on local DC capacitor can be achieved.
To control the sub-modules in a PWM mode, the resulted voltage reference is sent to the PWM modulation signal output unit. The PWM modulation signal output unit creates a PWM real-time modulation signal of the lower controller based on the voltage reference.
Impedance of the connection between each module of the cascaded rectifiers and the power grid is can be modified to be of inductance characteristic through adding a virtual inductor or placing a real inductor therein, and thus the input power transmission characteristic of the grid-connected with resistance characteristic can be represented as follows:
wherein Pi and Qi respectively represent the input active power and input reactive power of rectifier sub-module /, \Zime\ represents impedance modulus of the grid-connected, and Vg and Sg respectively represent the amplitude value and the phase angle of the voltage across the power grid.
In nominal state of the grid, since a power to be supplied to the load which single sub-module requires in a steady state is same, each sub-module outputs have a same input amplitude and phase angle, and the input active power and reactive power of rectifier sub-module i in the steady state can be simplified as
In combination with an expression of a power factor of the grid-connected,
, the operating voltage Vo in the steady state can be calculated in the case of the factor being a constant.
To verify the feasibility of the proposed control scheme, a low-voltage system including four cascaded modules is also implemented based on real-time HIL tests on OPAL-RT platform. The results of the real-time HIL tests are as shown in Fig. 3-4.
Fig. 3 shows from top to bottom waves of current ig of the power grid, input AC voltage vl-v4 of the four sub-modules, voltage Vdci of the DC capacitor, an operating frequency fi and a phase angle. From Fig. 3, the four cascaded sub-modules have the same amplitude, phase angle and frequency of the input voltage, and thus a balance of the voltage between the sub-modules is achieved. In the meantime, the voltage on the DC capacitor is kept at the reference of 200V, and the operating frequency of sub-module 1 is synchronized with the power grid to be at 50Hz. In this case, autonomous synchronization with the power grid and autonomous balance of the
voltage on the DC capacitor can be achieved.
In addition, as shown in Fig. 4, in a nominal voltage of the power grid, the four sub-modules absorb an active power of 4kW to maintain the consumption of loads at their back ends, and thus a balance of power absorption and load consumption can be reached. Moreover, the four sub-modules absorb reactive power compensation of 0.54kVar in the steady state, and in this case the power factor of the grid-connected of the cascaded rectifier system can be up to 0.992.
It should be understood that the embodiment disclosed herein is not limited to the specific structures or process steps disclosed herein, but should be extended equivalents of the technical features which persons skilled in the art can appreciate. It should be still understood, terms used herein are merely for describing specific embodiments and not intended to be limitation. “One embodiment” or “embodiments” mentioned in the description indicate that specific features, structures, or characteristics are involved in at least one embodiment of the present disclosure. Therefore, the phrases “one embodiment” or “embodiments” in each place throughout the description do not always mean the same embodiment.
Although the above examples are intended for explaining a principle of the present disclosure in one or multiple applications, for the person skilled in the art, it is obvious to make various modifications to formations, usages, or details of implementation without departing away from the concept and idea of the present disclosure on the condition that there is no need for inventive labors.

Claims (9)

1. Werkwijze voor hiërarchisch besturen van cascadegelijkrichters, omvattende de stappen van: genereren van een initialisatieparameterset in een hoger besturingsorgaan voor het opstarten van de cascadegelijkrichters; versturen, door het hogere besturingsorgaan, van de initialisatieparameterset naar meerdere lagere besturingsorganen via een communicatieverbinding, waarbij elk lager besturingsorgaan is ingericht om met een corresponderend exemplaar van submodules van de cascadegelijkrichters verbinding te maken en deze te besturen; genereren, in elk lager besturingsorgaan, van een PWMinitialisatiemodulatiesignaal gebaseerd op de ontvangen initialisatieparameterset, en zenden van het PWM-initialisatie-modulatiesignaal als een commando naar elke submodule in realtime om de cascadegelijkrichters op te starten, en in de tussentijd verzamelen van spanning en stroom naar een frontendingang en van een backenduitgang van de submodule nadat deze is gestart; verkrijgen, in elk lager besturingsorgaan, van een PWM-realtimemodulatiesignaal gebaseerd op verdere berekening op in realtime verzamelde waardes van spanning en stroom, en besturen van een spanning toegevoerd aan de submodule die daarmee corresponderend is verbonden door het PWM-realtimemodulatiesignaal; automatisch verbreken van een verbinding van een van de submodules met een systeem van de cascadegelijkrichters, wanneer abnormale spanning of stroom wordt gedetecteerd in genoemd ene exemplaar van de submodules door het lagere besturingsorgaan, en rapporteren van een foutbericht aan het hogere besturingsorgaan; en ontvangen, door het hogere besturingsorgaan, van het foutbericht, opnieuw genereren van een initialisatieparameterset en zenden daarvan naar elk lagere besturingsorgaan via een communicatieverbinding om de spanning toegevoerd aan elke resterende submodule in de cascadegelijkrichters van het elektriciteitsnetwerk opnieuw toe te wijzen.A method for hierarchically controlling cascade rectifiers, comprising the steps of: generating an initialization parameter set in a higher controller for starting the cascade rectifiers; sending, by the higher controller, the initialization parameter set to a plurality of lower controllers via a communication link, each lower controller being adapted to connect and control a corresponding copy of sub-modules of the cascade rectifiers; generating, in each lower controller, a PWM initialization modulation signal based on the received initialization parameter set, and sending the PWM initialization modulation signal as a command to each sub-module in real time to start the cascade rectifiers, and in the meantime collecting voltage and current to a front end input and a back end output of the sub-module after it has been started; obtaining, in each lower controller, a PWM real-time modulation signal based on further calculation on values of voltage and current collected in real time, and controlling a voltage applied to the sub-module correspondingly connected thereto by the PWM real-time modulation signal; automatically disconnecting one of the sub-modules from a cascade rectifier system when abnormal voltage or current is detected in said one instance of the sub-modules by the lower controller, and reporting an error message to the higher controller; and receiving, by the higher controller, the error message, regenerating an initialization parameter set and sending it to each lower controller via a communication link to reassign the voltage applied to each remaining sub-module in the cascade rectifiers of the electricity network. 2. Werkwijze voor het hiërarchisch besturen van cascadegelijkrichters volgens conclusie 1, waarbij de initialisatieparameterset een initialisatiespanningswaarde, een initialisatiefasehoek, en een nominaal-actief-vermogensreferentie omvat.The method for hierarchically controlling cascade rectifiers according to claim 1, wherein the initialization parameter set comprises an initialization voltage value, an initialization phase angle, and a nominal active power reference. 3. Werkwijze voor hiërarchisch besturen van cascadegelijkrichters volgens conclusie 2, waarbij de stap van het genereren van een initialisatieparameterset in een hoger besturingsorgaan voor het opstarten van de cascadegelijkrichters verder deelstappen omvat van: genereren van de initialisatiespanningswaarde en de initialisatie-fasehoek gebaseerd op een amplitudewaarde en een fasehoek van een gedetecteerde spanning van een elektriciteitsnetwerk; en verkrijgen van een nominaal-actief-vermogensreferentie gebaseerd op verdeling van belastingsvereisten.The method of hierarchically controlling cascade rectifiers according to claim 2, wherein the step of generating an initialization parameter set in a higher controller for starting the cascade rectifiers further comprises sub-steps of: generating the initialization voltage value and the initialization phase angle based on an amplitude value and a phase angle of a detected voltage from an electricity network; and obtaining a nominal asset power reference based on distribution of tax requirements. 4. Werkwijze voor hiërarchisch besturen van cascadegelijkrichters volgens conclusie 3, waarbij de stap van het verkrijgen van een PWM-realtimemodulatiesignaal verder deelstappen omvat van: berekenen van een huidig actief uitgangsvermogen van de submodule gebaseerd op de spanning en stroom gedetecteerd aan de frontendingang, om een fasehoekreferentie van een ingangsspanning te bepalen; bepalen van een amplitudereferentie van de ingangsspanning gebaseerd op een vermogensfactorindex van het verbonden netwerk; samenstellen van de fasehoek-referentie en de amplitude-referentie tot een spanningsreferentie toegevoerd aan de submodule vanuit het elektriciteitsnetwerk; en verkrijgen van het van het lagere besturingsorgaan naar de gelijkrichtersubmodules te zenden PWM-realtimemodulatiesignaal, gebaseerd op de spanningsreferentie.The method of hierarchically controlling cascade rectifiers according to claim 3, wherein the step of obtaining a PWM real-time modulation signal further comprises sub-steps of: calculating a current active output power of the sub-module based on the voltage and current detected at the front end input, determine a phase angle reference of an input voltage; determining an amplitude reference of the input voltage based on a power factor index of the connected network; compiling the phase angle reference and the amplitude reference into a voltage reference applied to the sub-module from the electricity network; and obtaining the PWM real-time modulation signal to be sent from the lower controller to the rectifier sub-modules based on the voltage reference. 5. Werkwijze voor hiërarchisch besturen van cascadegelijkrichters volgens conclusie 4, waarbij in de stap van het bepalen van een amplitude-referentie van de ingangsspanning gebaseerd op de vermogensfactorindex van het verbonden netwerk, een amplitude van de spanning toegevoerd aan de te besturen submodule wordt verkregen gebaseerd op de volgende vergelijking:The method of hierarchically controlling cascade rectifiers according to claim 4, wherein in the step of determining an amplitude reference of the input voltage based on the power factor index of the connected network, an amplitude of the voltage applied to the sub-module to be controlled is obtained based on on the following equation: in opstarttoestand,in startup state, in bedrijfstoestand,in operating condition, waarbij Vt de amplitudereferentie van de spanning toegevoerd aan gelijkrichtersubmodule i representeert, Vo de initialisatiespanningswaarde verschaft door het hogere besturingsorgaan representeert, waarbij Vo verschillende waardes in de opstarttoestand respectievelijk in de bedrijfstoestand heeft, en kan worden ingesteld gebaseerd op een aanpasbare netwerk-verbonden vermogensfactor in de bedrijfstoestand,wherein Vt represents the amplitude reference of the voltage applied to rectifier sub-module i, Vo represents the initialization voltage value provided by the higher controller, where Vo has different values in the start-up state and in the operating state, respectively, and can be set based on an adjustable network-connected power factor in the operating condition, Vg een amplitude van een realtime spanning over het elektriciteitsnetwerk representeert, Vg* een amplitude van een nominale spanning van het elektriciteitsnetwerk representeert, Nfcw het aantal modules dat deelneemt aan het compenseren voor fluctuatie van de spanning over het elektriciteitsnetwerk representeert, waarbij in het algemeen N/ew*10%N~20%N, waarbij iVhet aantal cascadegelijkrichtersubmodules representeert, en δ een verschil van de fasehoek tussen de cascadegelijkrichters en het elektriciteitsnetwerk in stationaire toestand is.Vg represents an amplitude of a real-time voltage across the electricity network, Vg * represents an amplitude of a nominal voltage of the electricity network, Nfcw represents the number of modules that participates in compensating for fluctuation of the voltage across the electricity network, with generally N / ew * 10% N ~ 20% N, where iV represents the number of cascade rectifier sub-modules, and δ is a difference of the phase angle between the cascade rectifiers and the electricity network in the stationary state. 6. Werkwijze voor hiërarchisch besturen van cascadegelijkrichters volgens conclusie 5, waarbij in de stap van het berekenen van het huidige reactieve vermogen afgegeven door de submodule gebaseerd op de spanning en stroom toegevoerd aan de frontend van de submodule, verzameld om de fasehoekreferentie van de ingangsspanning te bepalen, de fasehoek-referentie en frequentie van de spanning toegevoerd aan de te besturen submodule zijn verkregen gebaseerd op de volgende vergelijking:The method of hierarchically controlling cascade rectifiers according to claim 5, wherein in the step of calculating the current reactive power output from the sub-module based on the voltage and current applied to the front end of the sub-module, collected to determine the phase angle reference of the input voltage determine, the phase angle reference and frequency of the voltage applied to the sub-module to be controlled are obtained based on the following equation: waarbij oj, een hoekfrequentiereferentie van de spanning toegevoerd aan gelijkrichtersubmodule i representeert, co* een nominale hoekfrequentie van het elektriciteitsnetwerk representeert, kp een positieve versterking is, P* een toegevoerde actief-vermogensreferentie representeert, en in het algemeen P* wordt bepaald gebaseerd op een vermogen van de belasting, en Pi*, om een balans te verzekeren van een spanning op een gelijkstroomcondensator van de belastingkant, is ontworpen als:where oj, an angular frequency reference of the voltage applied to rectifier sub-module i, co * represents a nominal angular frequency of the electricity network, kp is a positive gain, P * represents an applied active power reference, and in general P * is determined based on a power of the load, and Pi *, to ensure a balance of a voltage on a load side DC capacitor, is designed as: waarbij Vdd een spanning op een condensator van de belastingkant van gelijkrichtersubmodule i representeert, V*,/c een nominale-spanningsreferentie van de condensator representeert, Po een nominaal-actief-vermogensreferentie representeert, kp en kj respectievelijk proportioneel-integraalcoëfficiënten zijn, en s een Laplace-operator is.where Vdd represents a voltage on a load side capacitor of rectifier sub-module i, V *, / c represents a nominal voltage reference of the capacitor, Po represents a nominal active power reference, kp and kj are proportional integral coefficients, and s is a Laplace operator. 7. Werkwijze voor hiërarchisch besturen van cascadegelijkrichters volgens conclusie 6, waarbij impedantie van de verbinding tussen elke submodule van de cascadegelijkrichters en het elektriciteitsnetwerk gewijzigd kan worden om een inductieve karakteristiek te hebbenThe method of hierarchically controlling cascade rectifiers according to claim 6, wherein impedance of the connection between each sub-module of the cascade rectifiers and the electricity network can be changed to have an inductive characteristic door het toevoegen van een virtuele spoel of plaatsing van een echte spoel daarin, en de ingangsvermogenstransmissiekarakteristiek van het verbonden netwerk met weerstandskarakteristiek als volgt gerepresenteerd kan worden:by adding a virtual coil or placing a real coil therein, and the input power transmission characteristic of the connected network with resistance characteristic can be represented as follows: waarbij P, and (h respectievelijk het toegevoerde actieve vermogen en toegevoerde reactieve vermogen van gelijkrichtersubmodule /' representeren, \ZHne\ de impedantiemodulus van het verbonden netwerk representeert, en Vg respectievelijk Óg de amplitudewaarde en de fasehoek van de spanning over het elektriciteitsnetwerk representeren.wherein P, and (h respectively represent the supplied active power and supplied reactive power of rectifier sub-module, \ ZHne \ represents the impedance modulus of the connected network, and Vg represent amplg or Óg respectively the amplitude value and the phase angle of the voltage across the electricity network. 8. Systeem voor hiërarchisch besturen van cascadegelijkrichters, omvattende: een hoger besturingsorgaan voor het genereren van een initialisatieparameterset en het zenden van de initialisatieparameterset via een communicatieverbinding om de cascadegelijkrichters op te starten, meerdere lagere besturingsorganen, elke communicatief verbonden met het hogere besturingsorgaan en corresponderend verbonden met een corresponderend exemplaar van submodules van de cascadegelijkrichters via een kabel, waarbij elk lager besturingsorgaan wordt gebruikt voor: genereren van een PWM-initialisatiemodulatiesignaal gebaseerd op de ontvangen initialisatieparameterset, en zenden van het PWM-initialisatiemodulatiesignaal als een commando naar elke submodule in realtime om de cascadegelijkrichters op te starten, en in de tussentijd verzamelen van een spanning en stroom toegevoerd/afgegeven door of aan een frontend/backend van elke submodule nadat deze is gestart; verkrijgen van een PWM-realtimemodulatiesignaal gebaseerd op verdere berekening op de in realtime verzamelde waardes van spanning en stroom, en besturen van een spanning toegevoerd aan de submodule die daarmee corresponderend is verbonden door het PWM-realtimemodulatiesignaal; en automatisch verbreken van een verbinding van een van de submodules met het systeem, wanneer abnormale spanning of stroom wordt gedetecteerd in genoemde ene exemplaar van de submodules, en rapporteren van een foutbericht naar het hogere besturingsorgaan, waarbij het hogere besturingsorgaan verder een foutverwerkingseenheid omvat voor het ontvangen van het foutbericht, het opnieuw genereren van een initialisatieparameterset en het zenden daarvan naar elk van de meerdere lagere besturingsorganen om de spanningA system for hierarchically controlling cascade rectifiers, comprising: a higher controller for generating an initialization parameter set and sending the initialization parameter set via a communication link to start the cascade rectifiers, multiple lower controllers, each communicatively connected to the higher controller and correspondingly connected with a corresponding copy of cascade rectifier sub-modules via a cable, each lower controller being used to: generate a PWM initialization modulation signal based on the received initialization parameter set, and send the PWM initialization modulation signal as a command to each sub-module in real time to start up cascade rectifiers, and in the meantime collect a voltage and current supplied / delivered by or to a frontend / backend of each sub-module after it has been started; obtaining a PWM real-time modulation signal based on further calculation on the values of voltage and current collected in real time, and controlling a voltage applied to the sub-module correspondingly connected to it by the PWM real-time modulation signal; and automatically disconnecting a connection from one of the submodules to the system when abnormal voltage or current is detected in said one instance of the submodules, and reporting an error message to the higher controller, the higher controller further comprising an error processing unit for the receiving the error message, regenerating an initialization parameter set and sending it to each of the multiple lower controllers for the voltage toegevoerd aan elke van de resterende submodules in de cascadegelijkrichters opnieuw toe te wijzen.reallocated to each of the remaining sub-modules in the cascade rectifiers. 9. Systeem voor hiërarchisch besturen van cascadegelijkrichters volgens conclusie 8, waarbij elk lager besturingsorgaan omvat: een actief-vermogensfrequentiebesturingseenheid, voor het berekenen van een huidig actief vermogen van de submodule gebaseerd op spanning en stroom van de frontendingang van de submodule om een fasehoekreferentie van ingangsspanning te bepalen; een reactief-vermogensspanningsbesturingseenheid, voor het bepalen van een amplitudereferentie van de ingangsspanning gebaseerd op vermogensfactorindex van het verbonden netwerk, een synthese-eenheid, voor het samenstellen van de fasehoekreferentie en de amplitudereferentie tot een spanningsreferentie toegevoerd aan de submodule; en een PWM-modulatiesignaaluitgangseenheid voor het verkrijgen van een vanuit het lagere besturingsorgaan te zenden PWM-realtime-modulatiesignaal gebaseerd op de spanningsreferentie.The hierarchical control system of cascade rectifiers according to claim 8, wherein each lower controller comprises: an active power frequency control unit, for calculating a current active power of the sub-module based on voltage and current from the front input of the sub-module to a phase angle reference of input voltage to decide; a reactive power voltage control unit, for determining an amplitude reference of the input voltage based on power factor index of the connected network, a synthesis unit, for compiling the phase angle reference and the amplitude reference to a voltage reference applied to the sub-module; and a PWM modulation signal output unit for obtaining a PWM real-time modulation signal to be sent from the lower controller based on the voltage reference.
NL2021570A 2018-08-14 2018-09-06 Method and system for hierarchically controlling cascaded rectifiers NL2021570B1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201810923110.3A CN108964488B (en) 2018-08-14 2018-08-14 Hierarchical control method and system for cascaded rectifier

Publications (1)

Publication Number Publication Date
NL2021570B1 true NL2021570B1 (en) 2019-05-08

Family

ID=64184150

Family Applications (1)

Application Number Title Priority Date Filing Date
NL2021570A NL2021570B1 (en) 2018-08-14 2018-09-06 Method and system for hierarchically controlling cascaded rectifiers

Country Status (2)

Country Link
CN (1) CN108964488B (en)
NL (1) NL2021570B1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL2026118B1 (en) * 2020-05-07 2021-11-23 Univ Central South Method and system of general decentralized control for cascaded inverters

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110138011B (en) * 2019-06-05 2020-06-30 合肥工业大学 Module power balance control method of cascaded photovoltaic solid-state transformer

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19963105A1 (en) * 1999-12-24 2001-06-28 Daimler Chrysler Ag Driving a bridging switch for current converter circuit with partial current converter systems e.g. for rail vehicles, involves connecting or decoupling partial current converter systems for certain operating situations
US20170222545A1 (en) * 2014-08-29 2017-08-03 Shindengen Electric Manufacturing Co., Ltd. Power factor improving converter, and power supply device including power factor improving converter
US20170229874A1 (en) * 2016-01-14 2017-08-10 Jabil Circuit, Inc. Low voltage, low frequency, multi level power converter
US20180212535A1 (en) * 2017-01-24 2018-07-26 Delta Electronics (Shanghai) Co., Ltd Cascade converter system and method of putting converter module of the same into operation

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19963105A1 (en) * 1999-12-24 2001-06-28 Daimler Chrysler Ag Driving a bridging switch for current converter circuit with partial current converter systems e.g. for rail vehicles, involves connecting or decoupling partial current converter systems for certain operating situations
US20170222545A1 (en) * 2014-08-29 2017-08-03 Shindengen Electric Manufacturing Co., Ltd. Power factor improving converter, and power supply device including power factor improving converter
US20170229874A1 (en) * 2016-01-14 2017-08-10 Jabil Circuit, Inc. Low voltage, low frequency, multi level power converter
US20180212535A1 (en) * 2017-01-24 2018-07-26 Delta Electronics (Shanghai) Co., Ltd Cascade converter system and method of putting converter module of the same into operation

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL2026118B1 (en) * 2020-05-07 2021-11-23 Univ Central South Method and system of general decentralized control for cascaded inverters

Also Published As

Publication number Publication date
CN108964488A (en) 2018-12-07
CN108964488B (en) 2021-01-19

Similar Documents

Publication Publication Date Title
AU2017352548B2 (en) Reactive power control method, device and system
US8068352B2 (en) Power inverter control for grid-tie transition
US7511385B2 (en) Power converters
CN103124077B (en) Suppress the system and method for generating set subsynchronous resonance
GB2432267A (en) Power converter for connecting a variable output generator to a supply network
Sarkar et al. Discrete time model predictive controller design for voltage control of an islanded microgrid
TW201633658A (en) Electrical power transmission network
NL2021570B1 (en) Method and system for hierarchically controlling cascaded rectifiers
CN107425745B (en) UPFC control system based on observer and MMC and control method thereof
CN107910869B (en) A kind of distribution static series compensator control system and its control method
CA2302344A1 (en) Method and device for improving the voltage quality of a secondary supply unit
Munir et al. Residential distribution system harmonic compensation using priority driven droop controller
Navarro-Rodríguez et al. Cooperative primary control of a hybrid AC/DC microgrid based on AC/DC virtual generators
CN109314395A (en) Improvement related with the interconnection of multiple renewable energy power generation factories
Liu et al. Stability criterion of droop-controlled parallel inverters based on terminal-characteristics of individual inverters
NL2021569B1 (en) Method and system for hierarchically controlling cascaded statcom system
Ghiasi et al. A control scheme based on virtual impedance and droop control to share power in an island microgrid
Nami et al. Hybrid HVDC system for offshore wind farms connection using series-connected diode rectifier units
Hussaini et al. Artificial neural network aided cable resistance estimation in droop-controlled islanded DC microgrids
US7202637B2 (en) Distributed control method
Sanchez Stability Investigation of Power Electronics Systems; A Microgrid Case
Raza et al. Converter applications for offshore network integrating wind energy
CN109660144A (en) A method of the three-phase inverter bi-mode control based on minimum variance adaptive structure
CN110134167A (en) Regulator and pressure regulation method
Jaraniya et al. Spearhead PV array based three phase charging station with multi EV spots using improved LP-PNLMS adaptive filter to support the power grid