CN104810855A - Current servo control method of inverter in multi-energy ship electric power system - Google Patents

Abstract

The invention relates to a current follow-up control method of an inverter in a multi-energy ship power system. This method is applied to a multi-energy ship AC power system composed of solar energy, diesel generators and energy storage systems, that is, the inverter is connected in parallel with the diesel generator to supply power for the ship load. The inverter works independently and generates electricity with diesel There are two modes of parallel operation of the inverter, that is: when the inverter operates independently, the voltage of the ship grid is controlled to be constant voltage and constant frequency, and the inverter is equivalent to a voltage source at this time; when the inverter operates in parallel with the diesel generator, The inverter realizes reactive power compensation for the ship grid, unbalanced load and load harmonic current function. The three-phase power of the diesel generator is balanced, and the output voltage of the inverter is determined by the output voltage of the diesel generator. At this time, the inverter Equivalent to a current source. The method of the invention combines the active and passive inverter technologies, solves the key problem of the inverter inverter technology in the multi-energy ship power system, and improves the quality of power supply.

Description

Current follow-up control method of inverter in multi-energy ship power system

technical field

The invention belongs to the field of ship power system and the field of power electronic conversion technology, in particular to a current follow-up control method of an inverter in a multi-energy ship power system.

Background technique

With the depletion of traditional fossil energy and the aggravation of environmental pollution, the trend of large-scale ships and automation is becoming more and more significant, and the proportion of high-power marine equipment that relies on electric drive and control continues to increase, energy issues have become constraints to the development of ship power systems. Bottleneck, it is necessary to study the green ship technology that will gradually replace traditional energy with renewable new energy with high efficiency, no environmental pollution, large amount and wide distribution. Based on the characteristics of ships sailing at sea, solar energy is the most direct, economical and effective new energy source, but there are defects such as unstable power supply, discontinuity, and changes with climate conditions. In order to improve the stability and flexibility of the ship's power supply system, the ship's multi-energy power system composed of new energy and traditional fossil energy can meet the greatly increased demand for ship energy and improve environmental pollution.

Compared with the land power grid, the ship power system usually adopts a three-phase three-wire system, the power grid capacity is small, and there is no common connection point with the large power grid, there are many high-power propulsion loads, frequency conversion devices, and nonlinear loads, some of which are similar to the capacity of the ship power system During the start-up process of large-capacity electrical equipment (such as side thrusters), the voltage and frequency of the ship's power grid will fluctuate, thereby reducing the power quality of the power grid. The decline in power quality will not only increase energy consumption, but also reduce the reliability of the power system and the safety margin of ship operation. These are also the differences between the ship power grid and the distributed micro-grid. From the perspective of the ship power system, the stability of the ship power grid voltage is determined by the excitation control system of the synchronous generator, and the frequency stability of the ship power grid is determined by the prime mover speed control system. A large voltage sag will cause the temperature of the stator winding of the asynchronous motor to rise, thereby accelerating the aging of the insulation, shortening the service life of the motor, and even burning out the motor in severe cases. At the same time, the voltage sag will reduce the transmission power of the transmission line, which will easily cause the instability of the system frequency. From the point of view of the power quality of the ship power grid, the grid harmonics caused by nonlinear loads and the three-phase unbalanced load are two important reasons that affect the power quality of the ship power grid. For the quality of power consumption of electric loads, the traditional three-phase four-wire system and the method of balancing the imbalance of each phase through the neutral line are difficult to apply to the ship power system dominated by the three-phase three-wire system.

Ship photovoltaic inverter is the key to realize the integration of new energy into the ship's AC power grid. As a channel for energy transmission, it undertakes the functions of voltage and current conversion and matching with the ship's power grid to realize the utilization of renewable energy, energy consumption and carbon emissions. decrease in volume. However, considering the limited laying area of ships and the low power conversion rate of photovoltaic cells, it is not realistic enough to use solar energy as a power source for ships. If the distributed grid-connected inverter technology in the land power grid is directly applied to the ship grid to maximize the use of new energy for power generation, and the insufficient power will be provided by the generator, there will be the following problems: ① solar power is highly dependent on the weather, The reliability of power supply is not high; ②The unstable power generation makes the generator operate in a large range and low efficiency, and the generator is likely to cause greater energy consumption; ③The load changes greatly, the voltage and fluctuation of the ship grid and the reactive power of the generator set The inherent problems of ships such as loss cannot be fundamentally improved, and the addition of inverters may further deteriorate the power quality of the grid. Obviously, for the marine photovoltaic and diesel-electric hybrid power supply system, it is necessary to study the inverter with simple circuit structure, high power density, high conversion efficiency, low cost, and suitable for the characteristics of the marine power grid. Frontier research topic on the combination of technology and new energy joint power supply technology.

Therefore, it is necessary to seek a multi-functional inverter control method suitable for a multi-energy ship AC power system composed of solar energy, diesel generators and energy storage systems, which has reactive power compensation and unbalanced load capacity. It is of great significance to improve the utilization rate of the generator, improve the quality of the inverter power supply current, and improve the power quality of the grid.

Contents of the invention

The purpose of the present invention is to provide a current follow-up control method for inverters in a multi-energy ship power system, which perfectly resolves the contradiction between the ship's limited volume and weight of equipment and the urgent need to improve the power quality of the ship's power grid , and fundamentally reduce the fluctuation of the voltage and frequency of the ship's power grid, and increase the output of the active power of the diesel generator.

In order to achieve the above purpose, the technical solution of the present invention is: a current follow-up control method for inverters in a multi-energy ship power system, which is applied to a multi-energy ship composed of solar energy, diesel generators and energy storage systems The power system is to connect the inverter and the diesel generator in parallel to supply power to the load of the ship. The inverter works in two modes: independent operation and parallel operation with the diesel generator, that is: when the inverter operates independently, it controls the ship power grid The voltage is constant voltage and constant frequency. At this time, the inverter is equivalent to a voltage source; when the inverter and the diesel generator are running in parallel, the inverter realizes reactive power compensation for the ship grid, unbalanced loads and load harmonics. Wave current function, the three-phase power balance of the diesel generator, the output voltage of the inverter is determined by the output voltage of the diesel generator, and the inverter is equivalent to a current source at this time.

In one embodiment of the present invention, when the inverter is running in parallel with the diesel generator, the inverter realizes reactive power compensation for the ship power grid by specifying the value of the active power and reactive power output by the inverter. Method implementation for determining the output current reference value.

In an embodiment of the present invention, when the inverter and the diesel generator operate in parallel, the specific process of the inverter realizing the unbalanced load of the ship power grid is as follows,

S31: Inverter A, B, C three-phase current control is phase-separated, and each phase current control is relatively independent;

S32: By having the same power difference as the load, determine the active power reference of the inverter by formula (1) with reactive power reference ;

Formula 1)

In the formula, P _LA , P _LB , P _LC , P _L (= P _LA + P _LB + P _LC ) are the three-phase power and total power of the loads A, B, and C respectively, and P _Inv and Q _Inv are the inverter reference active and reactive power;

S33: Active power reference obtained by step S32 with reactive power reference , combined with the frequency f and phase φ information of the voltage obtained after phase-locking the voltage of the ship power grid, to obtain the A, B, C three-phase fundamental current reference , , , the inverter realizes the capacity with unbalanced load.

In an embodiment of the present invention, when the inverter and the diesel generator are running in parallel, the specific process of the inverter providing the load harmonic current for the ship power grid is as follows:

S41: Load _currents i _LA , i _LB , i _LC obtain fundamental currents ifA _, ifB , _ifC after active filtering, and then combine fundamental currents ifA _, ifB , _ifC with load _currents i _LA , i Subtract _LB and i _LC to obtain harmonic current references i _hA , i _hB , i _hC ;

S42: The harmonic current references i _hA , i _hB , and i _hC obtained in step S41 are respectively compared with the fundamental current reference in step S33 , , By summing up, the reference of the inverter A, B, and C three-phase currents can be obtained, thereby realizing the load harmonic current compensation function of the inverter for the ship power grid.

In an embodiment of the present invention, when the inverter and the diesel generator run in parallel, the generator outputs three-phase balanced power under the unbalanced load condition of the three-phase power.

Compared with the prior art, the present invention has the following beneficial effects: the method of the present invention can not only transform the DC voltage generated by the new energy source into a high-quality sinusoidal alternating current that matches and is stable with the voltage of the ship power grid, but also can improve the power quality of the ship power grid Compared with the utilization rate of diesel generators and unbalanced load capacity, it has the advantages of bidirectional power flow, strong load adaptability, and wide application prospects; the control method of the present invention is applied to photovoltaic inverters in ship multi-energy power systems , stronger adaptability and superior comprehensive characteristics.

Description of drawings

Fig. 1 is a connection diagram of the ship's AC grid side in the present invention.

Fig. 2 is a schematic diagram of the current of the ship grid when the inverter and the diesel generator run in parallel according to the present invention.

Fig. 3 is a structural block diagram of the control circuit of the present invention.

Fig. 4 is a principle diagram of the output current reference of the inverter when the inverter of the present invention operates in parallel with the diesel generator.

Fig. 5 is a principle diagram of the output voltage reference of the inverter when the inverter operates independently in the present invention.

Detailed ways

The technical solution of the present invention will be specifically described below in conjunction with the accompanying drawings.

A current follow-up control method of an inverter in a multi-energy ship power system of the present invention, the method is applied to a multi-energy ship AC power system composed of solar energy, diesel generators and energy storage systems, that is, the inverter and diesel The generators are connected in parallel to supply power to the load of the ship. The inverter works in two modes: independent operation and parallel operation with diesel generators. The inverter is equivalent to a voltage source; when the inverter and the diesel generator run in parallel, the inverter realizes the reactive power compensation for the ship grid, with unbalanced load and the function of providing load harmonic current. The three-phase diesel generator In power balance, the output voltage of the inverter is determined by the output voltage of the diesel generator, and the inverter is equivalent to a current source at this time.

The implementation process of the present invention will be described in detail below.

The adoption of the control method of the invention enables the photovoltaic inverter to operate in parallel with the diesel generator, while improving the power quality of the ship power grid and the utilization rate of the diesel generator. The solar panel and the energy storage system are connected in parallel on the input side of the inverter. On the side of the ship's AC grid, the inverter and the diesel generator run in parallel to provide electric energy for the ship's load, as shown in Figure 1. The ship's AC power grid connects the diesel generator, inverter and load together, and the sum of the output current i _G of the diesel generator and the output current i _O of the inverter is equal to the load current i _L .

The current follow-up control method of the inverter in the multi-energy ship power system of the present invention is applied to the case where the ship inverter and the diesel generator operate in parallel to supply power, and the inverter can work independently and in parallel with the diesel generator. a working mode. When the inverter runs independently, it works in the passive inverter state, and the control target of the inverter is to keep the grid voltage at constant voltage and constant frequency, and has a strong load capacity; when the inverter and the diesel generator run in parallel , In addition to the basic function of integrating solar energy into the ship's power grid, the inverter can also realize three functions of reactive power compensation for the grid, unbalanced load, and load harmonic current supply. Taking one phase as an example, diesel power generation The principle waveforms of generator output current i _G , photovoltaic inverter output current i _O and load current i _L are shown in Figure 2, where the load current i _L contains a large number of harmonic currents, and the output current i _G of the diesel generator is A part of the fundamental wave current required by the load, while the inverter output current i o includes not only the remaining fundamental wave current required by the load, but also all the harmonic current required by the load.

The structural block diagram of the control circuit of the present invention, as shown in Figure 3, it includes the current reference generator, the load harmonic generator, the voltage reference generator when the inverter operates independently, and the voltage control switch, current controller, three-phase SPWM and three-phase inverter, and the control method and control parameters of A, B, C three-phase are exactly the same. The selection of the two operating modes of the inverter running independently and running in parallel with the diesel generator is realized by selecting a different current reference through the one-two switch, and the three one-two switches realize the mode selection through the same trigger signal Synchronize. When the inverter operates independently, the voltage reference generator generates three-phase reference voltages u _rA , u _rB , u _rC , and compares them with the inverter output voltages u _A , u _B , u _C respectively, and the voltage errors are sent to Voltage controller, the output of the voltage controller is used as the reference current i _rA , i _rB , i _rC output by the three-phase inverter after passing through the selector switch respectively. The three reference currents are respectively related to the inverter output current i _A , i After _B and i _C are compared, the current error is sent to the current controller, and the output u _eA , u _eB , u _eC of the current controller are used as the three-phase modulation wave of SPWM to generate the duty cycle required by the three-phase inverter. The empty ratio signals d _A , d _B , d _C , at this time the control circuit is a double closed-loop control system of voltage and current, which realizes the constant voltage and constant frequency output by the inverter, and the inverter is equivalent to a voltage source; when the inverter and diesel When the generators are running in parallel, the current reference generator and the load harmonic generator respectively generate the reference current of the three-phase inverter output fundamental current , , Reference current with load harmonic current , after the two parts of the current are added, they are used as the reference currents i _rA , i _rB , and i _rC output by the three-phase inverter through the selection switch respectively. As mentioned above, the control circuit constitutes a current closed-loop control system at this time to realize the constant current output by the inverter. The output voltage of the inverter is determined by the output voltage of the diesel generator, and the inverter is equivalent to a current source.

When the inverter and the diesel generator run in parallel, the inverter adopting the control circuit of the present invention can not only realize the basic function of integrating solar energy into the ship power grid, but also realize reactive power compensation for the power grid, and unbalanced load , Provide three functions of load harmonic current, three-phase power balance of diesel generator. Among them, the reactive power compensation of the grid is realized by the method of determining the output current reference value by giving the value of the inverter output active power and reactive power; the unbalanced load is controlled by the three-phase current of A, B, and C To realize, the current control of each phase is relatively independent; and the realization of the load harmonic current is realized by the load harmonic generator.

The principle of the inverter output current reference when the inverter and the diesel generator are running in parallel in the present invention is shown in Figure 4. The current reference signals of each phase ( i _rA , i _rB , i _rC ) are generated by the fundamental current reference ( , , ) and the load harmonic current ( i _hA , i _hB , i _hC ) are added. fundamental current reference ( , , ) generation principle is: according to the principle that the inverter phase power difference is the same as the load phase power difference, the active power P _INV and reactive power Q _INV are given by the inverter and the three-phase active power of the load detected ( P _LA , P _LB , P _LC ) and reactive power ( Q _LA , Q _LB , Q _LC ), formula (1) is established to determine the inverter active power reference ( ) with the reactive power reference ( ), and then through the detection of the effective value of the grid voltage, the current effective value of each item can be determined, and then the frequency f of the voltage and the phase φ information of each phase can be obtained after combining the phase-locking of the grid voltage, and the sine wave generator can be used to realize Three-phase fundamental current reference ( , , );

Formula 1)

In formula ₍ 1), PL _and Q _L are load active power and reactive power respectively, that is, PL = P _LA + P _LB + P _LC , Q _L = Q _LA + Q _LB + Q _LC .

The generation principle of the load harmonic current ( i _hA , i _hB , i _hC ) shown in Figure 4 of the present invention is: the load current ₍ i _LA , i _LB , i _LC ) is actively filtered to obtain the fundamental current ( ifA , i _fB , ifC ), and then subtract it from the load current to obtain _the harmonic current reference ( i _hA , i _hB , i _hC ). The harmonic current reference is added to the fundamental current reference respectively to obtain the reference of each phase current, thereby realizing the harmonic compensation function of the inverter for the load current.

When the inverter of the present invention operates independently, the principle of the inverter output voltage reference is shown in Figure 5. The phase-locked loop output frequency f and the frequency reference f _r determine the voltage reference frequency value through mode selection, and then the phase angle of each phase of the phase-locked loop and the given voltage reference effective value U _r are sent to the sine wave generator together to realize each phase voltage reference ( u _rA , u _rB , u _rC ). In order to realize the seamless switching of inverters from parallel operation to independent operation, the voltage reference needs to be pre-estimated when the inverters are running in parallel, so when the inverters are running in parallel, the voltage references of each phase ( u _rA , u The frequency and phase of _rB , u _rC ) must be consistent with the frequency and phase of phase locker output at all times, so as to minimize the impact on the power grid at the moment of switching and realize seamless switching. When the inverter runs independently, the frequency of the voltage reference is f _r , so as to ensure the constant frequency characteristic of the grid voltage.

The multifunctional inverter current follow-up control method of the present invention is based on the requirements of energy saving and environmental protection of ships, and applies power electronic power conversion technology to new energy generation technology of ships. According to the characteristics of large load and strong coupling of ship power systems, the active and The combination of passive inverter technology solves the key problems of inverter technology in the multi-energy ship power system and improves the quality of power supply. The inverter is a multifunctional inverter. In addition to realizing the power conversion from DC to AC, it can also be used as a three-phase load unbalance compensator, parallel active power filter, and reactive power compensator. This method is applied to inverters. The inverter will have broad application prospects on electric propulsion ships that have extremely strict requirements on the size and weight of electric equipment.

The above are the preferred embodiments of the present invention, and all changes made according to the technical solution of the present invention, when the functional effect produced does not exceed the scope of the technical solution of the present invention, all belong to the protection scope of the present invention.

Claims (5)

1. the electric current follow-up control method of inverter in a multiple-energy-source Ship Electrical Power System, the method is applied to the multiple-energy-source boats and ships AC electric power systems of solar energy, diesel engine generator and energy-storage system composition, be connected in parallel by inverter and diesel engine generator, for boats and ships load supplying, it is characterized in that: inverter be operated in independent operating, with diesel engine generator parallel running two kinds of patterns, that is: when inverter independent operating, controlling network of ship voltage is constant voltage constant frequency, and now inverter is equivalent to voltage source; When inverter and diesel engine generator parallel running, inverter realizes network of ship reactive power compensation, is with unbalanced load and provides load harmonic current function, diesel engine generator three-phase power balance, inverter output voltage is determined by diesel engine generator output voltage, and now inverter is equivalent to current source.

2. the electric current follow-up control method of inverter in multiple-energy-source Ship Electrical Power System according to claim 1, it is characterized in that: when inverter and diesel engine generator parallel running, it is determine that the method for output current fiducial value realizes by the value of given inverter active power of output and reactive power that described inverter realizes network of ship reactive power compensation.

3. the electric current follow-up control method of inverter in multiple-energy-source Ship Electrical Power System according to claim 1, it is characterized in that: when inverter and diesel engine generator parallel running, the detailed process that described inverter realizes the unbalanced load of network of ship band is as follows,

S31: inverter A, B, C three-phase current individual-phase control, and every phase current controls relatively independent;

S32: by there is the method for identical difference power with load, determine inverter active power benchmark by formula (1) , , with reactive power reference , , ;

formula (1)

In formula p _lA, p _lB, p _lC, p _l(= p _lA+ p _lB+ p _lC) be respectively load A, B, C three phase power and gross power, p _inv, q _invfor the given meritorious and reactive power of inverter;

S33: the active power benchmark obtained by step S32 , , with reactive power reference , , , in conjunction with the frequency to the phase-locked rear acquisition voltage of network of ship voltage fwith phase place φinformation, obtains A, B, C three-phase fundamental current benchmark , , , inverter realizes band unbalanced load ability.

4. the electric current follow-up control method of inverter in multiple-energy-source Ship Electrical Power System according to claim 1, it is characterized in that: when inverter and diesel engine generator parallel running, described inverter is embodied as network of ship provides the detailed process of load harmonic current as follows

S41: load current i _lA, i _lB, i _lCby obtaining fundamental current after active power filtering i _fA, i _fB, i _fC, by fundamental current i _fA, i _fB, i _fCagain with load current i _lA, i _lB, i _lCsubtract each other, harmonic current benchmark can be obtained i _hA, i _hB, i _hC;

S42: the harmonic current benchmark that step S41 is obtained i _hA, i _hB, i _hCrespectively with the fundamental current benchmark of step S33 , , be added, the benchmark of inverter A, B, C three-phase current can be obtained, thus achieve inverter and provide load harmonic current compensate function to network of ship.

5. the electric current follow-up control method of inverter in multiple-energy-source Ship Electrical Power System according to claim 1, it is characterized in that: when inverter and diesel engine generator parallel running, under three-phase power imbalance loading condition, generator exports three-phase equilibrium power.