1. Field of the Invention
The present invention relates to a technical field of an electrical power transmission and distribution, in particular to an automatic three-phase unbalanced load compensation experimental device and its control method.
2. The Prior Arts
Three-phase load unbalance has many adverse effects on power system. At present, people have done much research on three-phase unbalanced load compensation of the electrical power transmission and distribution system, focusing on the design of the reactive power compensation device body and the control strategies and methods of the reactive power compensation device. Due to lots of restrictive conditions, many advanced algorithms and control strategies are still deduced theoretically and simulated by the computer, and a few can be tested in site with much preparation and high cost. Therefore, a general, automatic three-phase unbalanced load compensation experimental platform is applicable to the test of various unbalanced load compensation strategies, and this experimental platform only can perform its function when there is a loading device. Reactive power compensation mainly aims at loads such as electric arc furnace, electric welding machine, electrified railway, etc. in industry. These loads can cause reactive power impact on the system in a short time, which causes serious three-phase unbalance of the system. When this type of load is simulated on the experimental platform, load variation must be controlled quickly and accurately. At the same time, lots of single-phase electrical equipment in the power system have strong randomness and uncertainty, so a load simulation experimental device which can connect/disconnect inductive load, capacitive load and resistive load in various topologies into/from the system quickly and accurately have great practical significance.
Aiming at the disadvantages of the prior art, the present invention provides an automatic three-phase unbalanced load compensation experimental device and its control method to simulate various actual industrial and civil loads in the laboratory and assess the compensation effect of the automatic compensation device. The experimental device and its control method of the present invention have strong simulation genuineness and low cost and are easy to achieve.
The purpose of the present invention is achieved by the following technical schemes: the automatic three-phase unbalanced load compensation experimental device of the present invention comprises an automatic compensation device, a load simulation part and a detection, display and control part. The automatic compensation device comprises a power capacitor and an intelligent grouping load switch; the load simulation part comprises A-phase load, B-phase load and C-phase load which have the same components, a switch power supply, an analog output module and a relay output module; the A-phase load, the B-phase load and the C-phase load each comprise a single-phase nonlinear reactor with fixed impedance, a magnetic control reactor with adjustable single-phase impedance, a single-phase capacitor, a single-phase resistor, a single-phase AC contactor, an anti-parallel thyristor and an intermediate relay; A-phase, B-phase and C-phase simulated loads are connected to the electrical network through a molded case circuit breaker; the detection, display and control part comprises a plurality of current transformers, a plurality of molded case circuit breakers, a three-phase digital display ammeter, a three-phase electric power monitoring instrument, a protocol conversion module (485 serial to Ethernet module), 485 buses (i.e., RS-485 buses). Ethernet cables and an upper computer. The upper computer controls the connection and disconnection of each simulated load of the load simulation part by operating the load simulation algorithm to assess the compensation effect of the automatic compensation device.
Circuit Connection:
The load simulation part is connected with the electrical network; the automatic compensation device is connected with the electrical network, connected with the load simulation part in parallel and located in front of the load simulation part; the three-phase digital display ammeter of the detection, display and control part is connected with the current transformer of the electrical network on the load simulation side; the three-phase electric power monitoring instrument of the detection, display and control part is connected with the access point electrical network of the automatic compensation device.
The automatic compensation device comprises a power capacitor and an intelligent grouping load switch; both ends of the power capacitor are respectively connected with the intelligent grouping load switch which is connected with the electrical network.
The load simulation part comprises A-phase load, B-phase load and C-phase load which have the same components, a switch power supply, an analog output module and a relay output module; the A-phase load, the B-phase load and the C-phase load each comprise a single-phase nonlinear reactor with fixed impedance, a magnetic control reactor with adjustable single-phase impedance, a single-phase capacitor, a single-phase resistor, a single-phase AC contactor, an anti-parallel thyristor and an intermediate relay; A-phase, B-phase and C-phase simulated loads are in star connection in accordance with the three phase four wire system and each consist of four branches connected in parallel. For the C-phase load, one end of the magnetic control reactor with adjustable single-phase impedance is connected with the single-phase AC contactor, the other end of the single-phase AC contactor is connected with one end of the anti-parallel thyristor, and the other end of the anti-parallel thyristor is connected with one end of the contact of the intermediate relay; one end of the single-phase nonlinear reactor with fixed impedance is connected to one end of the single-phase AC contactor, and the other end of the single-phase AC contactor is connected with one end of the contact of the intermediate relay; one end of the single-phase capacitor is connected to one end of the single-phase AC contactor, and the other end of the single-phase AC contactor is connected with one end of the contact of the intermediate relay; one end of the single-phase resistor is connected to one end of the single-phase AC contactor, and the other end of the single-phase AC contactor is connected with one end of the contact of the intermediate relay; the other end of the magnetic control reactor with adjustable single-phase impedance is connected with the other end of the single-phase nonlinear reactor with fixed impedance, and the other end of the single-phase capacitor is connected with the other end of the single-phase resistor; the other ends of the contacts of the intermediate relays are connected together and are connected with the neutral line; the A-phase load and the B-phase load have the same circuit connection with the C-phase load, and the A-phase load, the B-phase load and the C-phase load are in star connection and then are connected to the electrical network through the molded case circuit breaker.
The detection, display and control part comprises a current transformer, a molded case circuit breaker, a three-phase digital display ammeter, a three-phase electric power monitoring instrument, a protocol conversion module (485 serial to Ethernet module), 485 buses, Ethernet cables and an upper computer. The upper computer is communicated through Ethernet and is connected to the Ethernet interface of the protocol conversion module (485 serial to Ethernet module) by the Ethernet cable, the protocol conversion module (485 serial to Ethernet module) is respectively connected to the three-phase electric power monitoring instrument, the three-phase digital display ammeter, and the 485 communication terminal blocks of the analog output module and the relay output module of the load simulation part through 485 buses. The input end of the three-phase electric power monitoring instrument is connected with the output ends of the molded case circuit breaker and the current transformer, and the input ends of the molded case circuit breaker and the current transformer are connected to the electrical network; the input end of the three-phase digital display ammeter is connected with the output end of the current transformer, and the input end of the current transformer is connected with the electrical network; the output end of the analog output module of the load simulation part is connected to the control ends of the anti-parallel thyristors of the A-phase load, the B-phase load and the C-phase load, and the relay output module of the load simulation part is connected to the coil of the intermediate relay of each branch of the A-phase load, the B-phase load and the C-phase load; the input end of the switch power supply of the load simulation part is connected to the electrical network by a micro circuit breaker, and the output end is connected to the supply terminals of the analog output module and the relay output module.
The control part of the present invention mainly controls the connection and disconnection of simulated load and detects electrical quantity for parameter calculation.
The load simulation and effect control detection method of the present invention comprises the following steps:
In the Parameter Calculation Sub-process in Step 5, use the instantaneous reactive power theory to calculate the active power, the reactive power, the apparent power and the power factor of each load, and the total active power, the total reactive power, the total apparent power and the total power factor of three loads.
The instantaneous reactive power theory is based on the instantaneous value and is applicable to sine steady state and non-sine transient state. The traditional power theory is based on the average value and is only applicable to sine steady state. The device of the present invention uses the instantaneous reactive power theory and calculates the above parameters in accordance with three-phase instantaneous voltage and current.
Set ua, ub, uc, ia, ib and ic respectively as the acquired three-phase voltage and three-phase line current, and obtain uα, uβ, iα and iβ through conversion of A, B and C phases to α-β two phases.
Wherein
Synthesize vectors {right arrow over (uα)}, {right arrow over (uβ)}, and {right arrow over (iα)}, {right arrow over (iβ)} on the α-β plane respectively as (rotating) voltage vector {right arrow over (u)} and current vector {right arrow over (i)}.
{right arrow over (u)}={right arrow over (uα)}+{right arrow over (uβ)}=u∠φu,{right arrow over (i)}={right arrow over (iα)}+{right arrow over (iβ)}=i∠φi (2)
Wherein, u and i are respectively the module of vectors {right arrow over (u)} and {right arrow over (i)}; φu and φi are respectively the phase angle of vectors {right arrow over (u)} and {right arrow over (i)}.
Project the current vector {right arrow over (i)} on the voltage vector {right arrow over (u)} and its normal line, and obtain ip and iq which are respectively the instantaneous active current and the instantaneous reactive current of the three-phase circuit.
ip=i cos φ,iq=i sin φ (3)
Wherein, φ=φu−φi.
The product of u and ip is the instantaneous active power of the three-phase circuit, and the product of the u and iq is the instantaneous reactive power of the three-phase circuit.
p=uip,q=uiq (4)
Substitute Formula (3) in Formula (4) to obtain:
Wherein,
Substitute Formula (1) in Formula (5) to obtain:
The projections of the three-phase instantaneous power current on α axis and β axis are respectively the instantaneous power current of α phase and β phase:
Wherein, iαp and iβp are respectively the instantaneous active current of α phase and β phase; iαq and iβq are respectively the instantaneous reactive current of α phase and β phase.
The instantaneous power of α phase and β phase is respectively the product of instantaneous voltage and the instantaneous current of the related phase.
The power current of each phase of the three-phase circuit can be obtained by using the two-phase power current through conversion of α phase and β phase to A phase, B phase and C phase.
Wherein, C23=CαβT
Substitute Formula (7) in Formula (9) to obtain:
Wherein, A=(ua−ub)2+(ub−uc)2+(uc−ua)2
The instantaneous active power and the instantaneous reactive power of the A-phase load, the B-phase load and the C-phase load are:
The unbalance factor of the three-phase electric parameter is defined as the percentage of negative sequence component and positive sequence component of the three-phase phasor, and is represented by ε as:
Wherein, A1, and A2 are respectively the root-mean-square value of the positive sequence component and the negative sequence component.
Any group of three-phase asymmetrical phasors (such as voltage, current, etc.) can be resolved into three groups of symmetrical phasors: positive sequence component, negative sequence component and zero sequence component:
A simple method is that using the modules A and C of {dot over (A)} and Ċ and their included angle β can calculate the effective values of the positive sequence component and the negative sequence component as the following formula:
In the device of the present invention, the fundamental voltage amplitude values UA1 and UC1 and the phase angles φA1 and φC1 of the A-phase load and the C-phase load can be obtained from the process of harmonic analysis, and the expression of the unbalance factor of the three-phase fundamental voltage can be obtained from Formulae (13) and (14) to calculate the unbalance factor of the three-phase fundamental voltage:
To sum up, the parameter calculation sub-process comprises the following steps:
The load simulation control process of the present invention mainly simulates load and measures the response time and the compensation effect of the automatic compensation device of the experimental platform. The load simulation control process of the present invention comprises the following steps:
The load simulation sub-process of the present invention has the function of sending commands through the upper computer to control the relay and the anti-parallel thyristor to connect and disconnected the simulated load, and comprises the following steps:
The present invention has the advantages that the load simulation device is simple in structure, easy to achieve and easy to control through programming and has strong simulation genuineness, and the load simulation device can simulate actual load for industrial production including electric welding equipment, rolling mill, riser, winch, crane, electric arc furnace, large-scale convertor equipment, frequency control device, electric locomotive on electrified railway, etc.
The detailed structure, the operating principle and the control method of the automatic three-phase unbalanced load compensation experimental device of the present invention are described by figures and the embodiment as follows:
In the embodiment, the 220 V automatic three-phase unbalanced load compensation experimental platform used in the laboratory is taken as an example. The automatic compensation device consists of an intelligent grouping load switch and a power capacitor and can balance the three-phase unbalanced load with active power and compensate this load with reactive power.
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The embodiment gives a group of acquired data dynamically displayed by the computer:
The present invention gives the following typical simulated load types:
Load Type 1: Three-Phase Unbalanced Impact Load
Typical examples: electric welding equipment, rolling mill, riser, winch, crane, electric arc furnace, etc.
Typical examples: large-scale convertor equipment, frequency control device, household appliance, rolling mill, etc.
Typical examples: electric locomotive on electrified railway, and office equipment, such as computer printer, etc.
In the embodiment of the present invention, the types are as follows: current transformer—BH-0.66 75/5, molded case circuit breaker—DNM1-100 M/3300-80A, micro circuit breaker—DNB-63 2P C6A, single-phase AC contactor—DNLC1-D25 AC220V, intermediate relay—MY2NJ DC24V, switch power supply—AC220V/DV24V5A, analog output module—I-7024D DV24V, relay output module—I-7067D DV24V, three-phase digital display ammeter—PA1941-9K4, three-phase electric power monitoring instrument—PA2000-3, protocol conversion module—SK6000B, anti-parallel thyristor—CRS20KW, single-phase resistor—RXLG-5KW, single-phase capacitor—BSNG-8/0.525, magnetic control reactor with adjustable single-phase impedance—KTSG-20 kvar/0.4, single-phase nonlinear reactor with fixed impedance—BKSG-10 kvar/0.38, and automatic compensation device—LHRC-TB.
Number | Date | Country | Kind |
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2011 1 0249895 | Aug 2011 | CN | national |
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Number | Date | Country | |
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20130054204 A1 | Feb 2013 | US |