Transient and steady state power uniform control method for diesel generator set-inverter parallel power supply system
Technical Field
The application belongs to the technical field of micro-grid operation control, and particularly relates to a transient steady-state power equalization control method for a diesel generator set-inverter parallel power supply system.
Background
With the rapid development of renewable energy power generation technology, energy storage technology, micro-grid technology and the like, the construction of a wind-solar-diesel-storage multi-energy power generation micro-grid system becomes an effective technical approach for solving the power supply problem in remote areas. Different from a conventional synchronous machine power supply, distributed power supplies such as photovoltaic power, wind power and energy storage are often used as grid-connected interfaces through inverters, and diesel generator set-inverter parallel power supply becomes a typical power supply configuration of the independent micro-grid system.
In order to improve the safe and reliable operation performance of the system, in a diesel generator set-inverter parallel power supply system, a diesel generator set is generally used as a main power supply, a load maintains the stability of the voltage and the frequency of the system, an inverter is generally used as a slave power supply and is connected into the system in a current source mode, and the output power of the inverter is regulated through upper-layer energy management. Under the high-power load sudden change disturbance, an inverter which operates in a current source mode does not have the rapid power regulation capacity, so that the transient steady-state power equalization among heterogeneous power sources is difficult to realize in a diesel generator set-inverter parallel power supply system, the high-power load sudden change disturbance mainly depends on the response of the diesel generator set, and a severe challenge is brought to the voltage/frequency stability of a wind-solar-diesel energy storage multi-energy power generation micro-grid system containing a high-proportion power electronic power source.
Disclosure of Invention
Aiming at the defects of the prior art, the application provides a transient steady-state power equalization control method for a diesel generator set-inverter parallel power supply system, and aims to solve the problem of transient steady-state power equalization of the diesel generator set-inverter parallel power supply system under high-power load sudden change by introducing an active frequency modulation-reactive voltage regulation control mode to a phase-locked control-based inverter, and enhance the operation safety and stability of an independent microgrid heterogeneous power supply parallel power supply system.
In order to achieve the aim, the invention provides a transient and steady state power average control method for a diesel generator set-inverter parallel power supply system, which comprises the following steps:
1) the inverter detects the frequency of a power grid through a phase-locked loop;
2) the inverter detects and calculates the voltage amplitude of the terminal of the inverter, the active power output by the inverter and the reactive power output by the inverter;
3) the diesel generator set detects and calculates the rotating speed of a generator per se, the voltage amplitude of the terminal of the generator per se, the active power output per se and the reactive power output per se;
4) the inverter adopts an active frequency modulation droop strategy, and adjusts a d-axis current instruction through a PID controller;
5) the inverter adopts a reactive power voltage regulation droop strategy and regulates a q-axis current instruction through a PI (proportional integral) controller;
6) the diesel engine set adopts an active frequency modulation droop strategy, and the mechanical power output by the diesel engine is regulated through a speed regulator;
7) the diesel generator set adopts a reactive voltage regulation droop strategy, and the excitation voltage of the generator is regulated through an excitation controller.
Further, the control logic of step 4) is:
the inverter adjusts an inverter output current d-axis current instruction through droop control and PID control based on self output active power and grid frequency obtained through detection and calculation, and the expression is as follows:
in the formula id_refIs an inverter d-axis current command, omega, per unit valuerefIs the set value of the inverter frequency, k, per unit valuepFor active frequency-modulated droop coefficient, PinvOutputting active power per unit value for inverterAnd omega is the per unit value of the power grid frequency detected by the phase-locked loop, kp1Proportionality coefficient, k, of active frequency-modulated PID controlleri1Is the integral coefficient, k, of an active frequency modulation PID controllerd1Is the differential coefficient, T, of an active frequency-modulated PID controller1And controlling the time constant of the delay link for the active current instruction.
Further, the control logic of step 5) is as follows:
the inverter adjusts an inverter output current q-axis current instruction through droop control and PI control based on self output reactive power and self terminal voltage amplitude obtained through detection and calculation, and the expression is as follows
In the formula iq_refIs an inverter q-axis current command, U, per unit valuerefIs the voltage command value of the inverter terminal under the per unit value, kqFor reactive voltage regulation of droop coefficient, QinvOutput reactive power per unit value, U, for the inverterinvIs the voltage amplitude of the inverter terminal at a per unit value, kp2Proportionality coefficient, k, of reactive voltage-regulating PI controlleri2For the integral coefficient, T, of reactive voltage-regulating PI controllers2And controlling the time constant of the delay link for the reactive current instruction.
Further, the control logic of step 6) is:
the diesel generating set adjusts the mechanical power of a prime motor through droop control and speed regulation control based on the self output active power and the self generator rotating speed obtained through detection and calculation, and the expression is as follows:
Tm=(ωref-kpPsg-ωsg)Ggov(s) (3)
in the formula, TmOutputting mechanical power omega for prime mover of diesel generator set under per unit valuerefIs the rotational speed instruction value, k, of the diesel generator set under the per unit valuepFor active frequency-modulated droop coefficient, PsgOutputting an active power per unit value, omega, for a diesel generator setsgGenerating set for firewoodPer unit value of rotation speed, Ggov(s) is the governor dynamic transfer function.
Further, the control logic of step 7) is:
the diesel generator set adjusts the excitation voltage through droop control and excitation control based on self output reactive power and self terminal voltage amplitude obtained through detection and calculation, and the expression is as follows:
Ef=(Uref-kqQsg-Usg)Gexc(s) (4)
in the formula, EfIs the excitation voltage of the diesel generator set under per unit value, UrefIs the end voltage instruction value, k, of the diesel generator set under the per unit valueqFor reactive voltage regulation of droop coefficient, QsgOutputting reactive power per unit value, U, for a diesel generating setsgVoltage amplitude at the end of the diesel generator set per unit value, Gexc(s) is the excitation control dynamic transfer function.
Compared with the prior art, the invention has the beneficial effects that:
(1) by introducing an active frequency modulation control strategy into the inverter, the transient and steady state equipartition performance of the active power of the diesel generator set-inverter parallel power supply system under the condition of high-power load sudden change is enhanced, and the frequency stability of the system is enhanced;
(2) by introducing a reactive voltage regulation control strategy into the inverter, the transient and steady state equipartition performance of the reactive power of the diesel generator set-inverter parallel power supply system under the condition of high-power load sudden change is enhanced, and the voltage stability of the system is enhanced;
(3) only need on the basis of current source mode dc-to-ac converter, increase active frequency modulation-reactive voltage regulation outer loop control and adjust dq axle current instruction, need not additionally to increase hardware equipment and modify the communication mode, conveniently upgrade and reform transform current dc-to-ac converter, easily promote, the direct engineering application of being convenient for.
Drawings
FIG. 1 is a schematic diagram of a diesel generator set-inverter parallel power supply system;
fig. 2 is a schematic diagram of a transient and steady state power equalization control method for a diesel generator set-inverter parallel power supply system provided by the invention;
FIG. 3 is a schematic diagram of a simulation system for verifying the validity of the proposed method;
FIG. 4 is a schematic diagram of the active power dynamics of a diesel generator set-inverter under the condition of sudden change of a high-power load;
FIG. 5 is a schematic diagram of a diesel generator set-inverter reactive power dynamic under a high-power load sudden change;
FIG. 6 is a schematic diagram of bus voltage amplitude dynamics under sudden change of high-power load;
fig. 7 is a schematic diagram of system frequency dynamics under sudden change of high-power load.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application. In addition, the technical features mentioned in the embodiments of the present application described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 shows an application scenario of the present invention: a diesel generator set-inverter parallel power supply system in an independent micro-grid. FIG. 2 shows a technical solution of the present invention, in which an inverter is connected in parallel with a diesel generator set in a current source mode, and detects a frequency change of a power grid based on a phase-locked loop, and the inverter is controlled and regulated to output an active current instruction through active frequency modulation droop; detecting the voltage amplitude change of the terminal of the inverter, and controlling and regulating the inverter to output a reactive current instruction through reactive voltage regulation droop; the diesel generator set adopts an active frequency modulation droop strategy to adjust the output mechanical power of a prime motor, and adopts a reactive voltage modulation droop strategy to adjust the power generation excitation voltage; therefore, the transient and steady power sharing of the inverter and the diesel generator set under the condition of high-power load sudden change is realized.
The transient steady state power average control method for the diesel generator set-inverter parallel power supply system, as shown in fig. 2, comprises the following steps:
1) the inverter detects the frequency of a power grid through a phase-locked loop;
2) the inverter detects and calculates the voltage amplitude of the terminal of the inverter, outputs active power and outputs reactive power;
3) detecting and calculating the self rotating speed, the terminal voltage amplitude, the output active power and the output reactive power by the diesel generator set;
4) the inverter adjusts an inverter output current d-axis current instruction through droop control and PID control based on self output active power and grid frequency obtained through detection and calculation, and control logic is shown as the following formula:
in the formula id_refIs an inverter d-axis current command, omega, per unit valuerefIs the set value of the inverter frequency, k, per unit valuepFor active frequency-modulated droop coefficient, PinvOutputting an active power per unit value for the inverter, wherein omega is a power grid frequency per unit value detected by the phase-locked loop, and kp1Proportionality coefficient, k, of active frequency-modulated PID controlleri1Is the integral coefficient, k, of an active frequency modulation PID controllerd1Is the differential coefficient, T, of an active frequency-modulated PID controller1And controlling the time constant of the delay link for the active current instruction.
When the active load suddenly increases, the rotating speed of the diesel generator set can be reduced, the frequency of a power grid can be reduced, the inverter active frequency modulation outer ring PID controller detects frequency deviation, and the d-axis current instruction is rapidly increased so that the inverter can rapidly respond to transient active power shortage; when the active load is suddenly unloaded, the rotating speed of the diesel generator set can be increased, the frequency of a power grid can be increased, the inverter active frequency modulation outer ring PID controller detects frequency deviation, and a d-axis current instruction is rapidly reduced so that the inverter can rapidly respond to transient active power surplus; the steady-state active power between the inverter and the diesel generator set is realized by active frequency droop control.
5) The inverter adjusts an inverter output current q-axis current instruction through droop control and PI control based on self output reactive power and self terminal voltage amplitude obtained through detection and calculation, and control logic is shown as the following formula:
in the formula iq_refIs an inverter q-axis current command, U, per unit valuerefIs the voltage command value of the inverter terminal under the per unit value, kqFor reactive voltage regulation of droop coefficient, QinvOutput reactive power per unit value, U, for the inverterinvIs the voltage amplitude of the inverter terminal at a per unit value, kp2Proportionality coefficient, k, of reactive voltage-regulating PI controlleri2For the integral coefficient, T, of reactive voltage-regulating PI controllers2And controlling the time constant of the delay link for the reactive current instruction.
When reactive load suddenly increases, the voltage of a system bus can be reduced, so that the voltage amplitude of the voltage of the inverter terminal is reduced, the voltage deviation is detected by the inverter reactive voltage regulation outer ring PI controller, and the q-axis current instruction value is quickly increased to enable the inverter to quickly respond to transient reactive power shortage; when the reactive load is suddenly unloaded, the voltage of a system bus can be increased, so that the voltage amplitude of the voltage of the inverter terminal is increased, the voltage deviation is detected by the inverter reactive voltage regulation outer ring PI controller, and the q-axis current instruction is quickly reduced so that the inverter can quickly respond to the transient reactive power excess; the steady-state reactive power between the inverter and the diesel generator set is uniformly controlled by reactive voltage regulation and droop.
6) The diesel generating set adjusts the mechanical power of a prime motor through droop control and speed regulation control based on the self output active power and the self generator rotating speed obtained through detection and calculation, and the control logic is as follows:
Tm=(ωref-kpPsg-ωsg)Ggov(s) (3)
in the formula, TmOutputting mechanical power omega for prime mover of diesel generator set under per unit valuerefIs the rotational speed instruction value, k, of the diesel generator set under the per unit valuepFor active frequency-modulated droop coefficient, PsgOutputting an active power per unit value, omega, for a diesel generator setsgIs the per unit value of the rotating speed of the diesel generating set Ggov(s) is the governor dynamic transfer function.
When the active load suddenly increases, the rotating speed of the diesel engine set can be reduced, the speed regulator of the diesel engine set detects the rotating speed deviation, and the mechanical power output by the prime motor is increased so that the diesel engine set responds to the transient active power shortage; when the active load is suddenly unloaded, the rotating speed of the diesel engine set can rise, the speed regulator of the diesel engine set detects the rotating speed deviation, and the mechanical power output by the prime motor is reduced so that the diesel engine set responds to the excess of transient active power; the steady-state active power between the inverter and the diesel generator set is realized by active frequency droop control.
7) The diesel generator set adjusts the excitation voltage through droop control and excitation control based on self output reactive power and self terminal voltage amplitude obtained through detection and calculation, and the control logic is as follows:
Ef=(Uref-kqQsg-Usg)Gexc(s) (4)
in the formula, EfIs the excitation voltage of the diesel generator set under per unit value, UrefIs the end voltage instruction value, k, of the diesel generator set under the per unit valueqFor reactive voltage regulation of droop coefficient, QsgOutputting reactive power per unit value, U, for a diesel generating setsgVoltage amplitude at the end of the diesel generator set per unit value, Gexc(s) is the excitation control dynamic transfer function.
When the reactive load suddenly increases, the voltage of a system bus can be reduced, so that the voltage amplitude of the voltage of the diesel generator set is reduced, the excitation control of the diesel generator set detects the voltage deviation, and the excitation voltage of the generator is increased to enable the diesel generator set to respond to the transient reactive power shortage; when the reactive load is suddenly unloaded, the voltage of a system bus can be increased, so that the voltage amplitude of the voltage of the diesel generator set is increased, the excitation control of the diesel generator set detects the voltage deviation, and the excitation voltage of the generator is reduced to enable the diesel generator set to respond to the transient reactive power excess; the steady-state reactive power between the inverter and the diesel generator set is uniformly controlled by reactive voltage regulation and droop.
A simulation model shown in FIG. 3 is built in PSCAD/EMTDC to verify the performance of the control method provided by the application. The capacity of the diesel generator set and the capacity of the inverter in the simulation model are both 500kVA, and the rated value of line voltage is 400V; the inductance value of the inductance-resistant load 1 is 1.2mH, and the resistance value is 0.5 omega; the inductance value of the inductance-resistance load 2 is 0.96mH, and the resistance value is 0.4 omega. The system is in a stable state before 40s, BK1-BK5 is in a closing state, BK6 is in an opening state, and the diesel generating set and the inverter are connected in parallel with a load 1. At 40s, the BK6 is switched on, the inductance-resistance load 2 is put into use, and the system carries out high-power load sudden addition; at 50s, BK6 is switched off, the inductance-resistance load 2 is cut off, and the system carries out high-power load sudden unloading.
The simulation results of fig. 4 to 7 show that when the high-power load is suddenly increased or decreased, the transient and steady power sharing between the diesel generator set and the inverter can be realized, and the voltage frequency stability of the system is enhanced.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.