CN203645340U - Power conversion system of mobile energy storage - Google Patents

Abstract

The utility model discloses a power conversion system of mobile energy storage. The power conversion system of mobile energy storage comprises a main circuit and a controller, and a DC bus of the main circuit is connected with a battery pack and is connected with a voltage source converter via a switch element and a filter capacitor. The voltage source converter is connected with a power grid via a grid side filter and a grid connected switch, and the filter capacitor is in parallel connection with a pre-charging circuit. The controller comprises a core controller, and a grid side ADC module, a DC side ADC module and a driving and power protection circuit which are connected with the core controller. By the reasonable parameter design and the connection mode, the connection reliability from the battery pack to the power grid is guaranteed, thereby guaranteeing that a whole mobile energy storage device works safely and reliably.

Description

The power conversion system of mobile energy storage

Technical field

The utility model relates to the power conversion system that connects electrical network and battery pack in large power energy storage equipment.

Background technology

Energy storage power conversion system PCS is the mutual critical component of battery energy storage carrier and electrical network, pass through PCS, energy-storage battery obtains energy or exports energy to AC network from AC network, under discharge condition, the direct current energy in battery pack carries out energy conversion by PCS, and direct current energy is transformed to AC energy feedback grid, in charged state, PCS, by energy conversion, is transformed to direct current energy by AC energy, charges the battery.Mobile energy-accumulating power station by PCS for 100kw, therefore needs to design suitable connected mode, and by rational control unit, guarantees the reliability and stability of whole mobile energy storage device.

Utility model content

Technical problem to be solved in the utility model is to realize a kind of PCS on electrical network that is connected to that guarantees that high-power mobile energy storage device can be safe and reliable.

To achieve these goals, the technical solution adopted in the utility model is: a kind of power conversion system of mobile energy storage, comprise main circuit and controller, the DC bus of described main circuit connects battery pack and is connected to voltage source converter through switch element, filter capacitor, described voltage source converter is connected to electrical network through net side filter, grid-connected switch, and described filter capacitor is parallel with pre-charge circuit;

Described controller comprises core controller; and the net side ADC module, DC side ADC module, driving and the power protecting circuit that are connected with core controller; described net side ADC module connects the grid-connected switch of VSC current on line side collecting unit, PCS net side; and voltage acquisition unit on electrical network; described DC side ADC module connects DC capacitor voltage collecting unit, DC bus current collecting unit.

Described net side filter is to be by two inductance and a LCL filter that electric capacity forms, and L is current transformer side inductance value value 145-155 μ H, and LS is net side inductance value value 295-305 μ H, electric capacity value 6.2-6.5 μ F.

Described filter capacitor $C_{\mathrm{dc}}\≥\frac{2\×\mathrm{\ΔP}\×t}{{(U_{\mathrm{dc}}+\mathrm{\ΔU})}^2-{U_{\mathrm{dc}}}^2}=2.225\mathrm{mF};$

Wherein: P is 100kW, Δ P is 100kWX50%=50kW, and t gets 20 switch periods, and switching frequency is got 8kHz.

Described filter capacitor value 2.5mF.

Described switch element and grid-connected switch adopt IGBT, each described IGBT adopt model be the 2MBI600VN of Fuji ?120 ?50, its withstand voltage is 1200V, it is maximum that to allow direct current be 600A.

Described core controller is through CAN connected system transmission monitor.

Described core controller comprises fpga chip, DSP, power circuit and real-time ethernet interface.

Described core controller is also provided with RS232 interface, and connects input equipment by RS232 interface.

The utility model has the advantage of by rational parameter designing, and connected mode, guarantee that battery pack is connected to the reliability of electrical network, thereby ensured the safe and reliable operation of whole mobile energy storage device.

Brief description of the drawings

Below the mark in content and figure that in the utility model specification, every width accompanying drawing is expressed is briefly described:

Fig. 1 is the main circuit topological structure of pcs system;

Fig. 2 is control system module map;

Fig. 3 is the simplification single phase circuit model of PCS;

Embodiment

For the mobile energy-accumulating power station of this project 100kW, adopt the structure of single stage type comparatively suitable, system configuration as shown in Figure 1, the power conversion system of mobile energy storage comprises main circuit and controller, the DC bus of main circuit connects battery pack and is connected to voltage source converter (VSC) through switch element, filter capacitor, this voltage source converter is connected to electrical network through net side filter, grid-connected switch, and filter capacitor is parallel with pre-charge circuit.PCS DC bus termination enters storage battery, make VSC four quadrant running by the modulation ratio m and the merit angular difference δ that change VSC, can be equivalent to generalized impedance converter, also can regard modified model STATCOM as, provide two-way controlled meritorious, idle, to control stablizing of voltage that PCC order and frequency.

The simplification single phase circuit model of PCS as shown in Figure 3, PCS is by detecting amplitude and the phase place of AC voltage, regulate current amplitude and the phase place of injected system access point (PCC point), thereby realize the two-way flow of energy between DC side and AC, namely can four quadrant running, realize two-way meritorious, the reactive power exchange between energy-storage units and electric power system, thereby there is the performance of net side power factor controlling, energy transmitted in both directions.In the time that PCS draws electric energy from electrical network, it runs on rectification operating state; When PCS is during to electrical network electric energy transmitting, it runs on inversion operating state.

PCS has the function of analog measurement, and can survey analog quantity be converted into digital quantity by ADC module and coherent signal treatment circuit and send into CPU and calculate, thereby the specific function of realization is specific as follows:

(1) DC voltage

PCS should have DC voltage testing circuit, and this circuit can detect in real time to DC voltage.

(2) inverter output current

PCS should have inverter output three-phase current detection circuit, and amplitude, phase place, aberration rate that this circuit can be exported three-phase current to inverter detect in real time.

(3) PCC place three-phase voltage

PCS should have PCC place three-phase voltage testing circuit, and this circuit can detect in real time to the amplitude of PCC place three-phase voltage, phase place, aberration rate, degree of unbalance.

(4) charging and discharging currents

PCS should have charging and discharging currents testing circuit, and this circuit can detect in real time to the amplitude of charging and discharging currents, phase place.

Net side filter should adopt LCL filter, need to design the inductance value of two inductance and the capacitance of an electric capacity.The major function that net is surveyed filter is filtering high order harmonic component, and filter inductance is larger, and filter effect is better, but along with inductance increases, the dynamic property meeting variation of system, system cost and volume also can raise.In the time that filter capacitor increases, filter effect can be strengthened, but system resonance frequency can reduce, if resonance frequency is reduced to fundamental frequency, can affect the stability of system.And, increase electric capacity and can make the absorption of LCL filter more idle.

When design, to meet the requirement of harmonic current value and total harmonic distortion coefficient (THD), especially harmonic wave current transformer being produced at switching frequency place will have good filtration result, conventionally weigh the content of certain specific subharmonic in unsinusoidal periodic quantity than d with harmonic attenuation, the harmonic attenuation ratio of General Requirements current on line side is limited in below 0.2.Under the prerequisite that meets above-mentioned designing requirement, should reduce used inductance, capacitance as far as possible, thus cost-saving, reduce equipment volume, improve on the other hand the dynamic property of system.

Above-mentioned design standard is followed in the design of LCL filter, conventionally adopts following distribution design method:

(1) determine the span of total inductance LT: be to improve the follow-up control of electric current and the response speed of system, the value of inductance L T is the smaller the better.But the value of inductance is larger, the filter effect of filter can be better.Therefore, need to consider and select suitable value:

$\frac{U_{\mathrm{dc}}}{4\sqrt{3}{i}_{\mathrm{ripm}}{f}_{\mathrm{sw}}}\≤L_T\≤\frac{\sqrt{\frac{{U_{\mathrm{dc}}}^2}{3}-E_m^2}}{{\mathrm{\ωI}}_{\mathrm{sm}}}$

Wherein, i _ripmbe harmonic current peak value, be generally 15% of fundamental current peak value, Em is electrical network phase voltage peak value; Ism is electrical network phase current peak value; Fsw is the switching frequency of rectifier; ω is the angular frequency of line voltage.

(2) determine capacitor C f span: too low for fear of rectifier power factor, the First Harmonic Reactive Power that general filter capacitor absorbs can not be greater than 5% of the specified active power of system:

$C_f<5\%\frac{P_n}{3\&CenterDot;2\mathrm{\&pi;f}\&CenterDot;E^2}$

Wherein, Pn is the active power that under rated condition, system absorbs; F is the frequency of line voltage; E is the effective value of electrical network phase voltage.

(3) determine each parameter of filter than d according to harmonic attenuation: make r=LS/L, set the value of d, filter capacitor C _fand inductance L _t, judge that following quadratic equation has or not normal solution:

${\mathrm{dr}}^2+(2d+1-d{\mathrm{\&omega;}}_{\mathrm{sw}}^2{L}_T{C}_f)r+d+1=0$

If equation does not have normal solution can change the value of d, Cf, TL, until equation has normal solution.

Wherein, L is current transformer side inductance value, L _sfor net side inductance value.

(4) judge whether resonance frequency meets the demands, if do not met, return to the 3rd step and redesign.For avoiding resonance to occur near main harmonic frequency, resonance frequency need meet:

10f _n≤f _res≤0.5f _sw

Wherein, $f_{\mathrm{res}}=\frac{1}{2\mathrm{\&pi;}}\sqrt{\frac{(L+L_S)}{{\mathrm{LL}}_S{C}_f}}$

For the PCS of this project 100kW, design filtering total inductance is 0.1pu, and so, filtering total inductance is:

$L_T=0.1\mathrm{pu}/(\sqrt{3}\&times;\mathrm{\&omega;}\&times;I_{\mathrm{SN}})=0.1\&times;380/(\sqrt{3}\&times;2\mathrm{\&pi;}\&times;50\&times;151.93)=0.46\mathrm{mH}$

The preferred value of design L and LS is L=150 μ H, LS=300 μ H.

Getting resonance frequency is 2kHz, and capacitor design is:

$C_f=\frac{L+L_S}{{\mathrm{LL}}_S{\left(2\mathrm{\&pi;}{f}_{\mathrm{res}}\right)}^2}=63.3\mathrm{\&mu;F}$

In Fig. 3: e is net side input ac power, i.e. PCC place voltage; I is net side input current, i.e. PCC place electric current; L is the inductance of reactor and circuit; R is AC equivalent resistance; U is AC voltage, i.e. current transformer output voltage; Udc is DC voltage; Idc is DC side electric current; Cdc is intermediate supports electric capacity (filter capacitor).

Filter capacitor major function is:

(1) stablize the energy exchange between grid-connected converter AC and DC side load, and the voltage of stable grid-connected converter DC side;

(2) suppress DC side harmonics voltage.

In general, DC bus capacitor need to be considered the factor of two aspects: meet Voltage loop control followability, meet direct voltage anti-interference.For choosing of DC support electric capacity, with regard to voltage follow, capacitance should be as far as possible little, and capacitance is less, and Voltage loop regulates the speed of DC voltage faster, and voltage follow is better, and the dynamic response of voltage is good; With regard to anti-interference, capacitance should be tried one's best greatly, and capacitance is larger, and the fluctuation of DC voltage is less, and its anti-interference is better.

Consider stable situation.For adopting three-phase SVPWM modulation grid-connected converter, in stable operation situation, its effective value that flows through the ripple current of DC bus capacitor is generally approximately and exchanges 55% of phase current effective value, ripple voltage in engineering on general permission electric capacity is 1% of middle dc voltage rated value, and DC bus capacitor should meet following formula:

$C_{\mathrm{dc}}\&GreaterEqual;\frac{I_{\mathrm{rms}}}{2\mathrm{\&pi;}\&times;U_{\mathrm{rms}}\&times;f_s}=\frac{0.55I_s}{2\mathrm{\&pi;}\&times;0.01U_{\mathrm{dc}}\&times;f_{\mathrm{sw}}}$

Wherein, Irms is the ripple current that flows through DC support electric capacity;

IS is phase current effective value;

Urms is the ripple voltage on DC support electric capacity;

Udc is middle dc voltage rated value;

Fsw is the switching frequency of grid-connected converter;

Consider the situation that current transformer load increases suddenly.In the time that current transformer load increases suddenly, in current transformer Voltage loop pi regulator allocating time t, the Power supply that the needed instantaneous energy of load is all stored up by DC support capacitor memory, until voltage-regulation works.In order to meet the requirement of dynamic response performance, suppose that current transformer load increases by 50% suddenly, Voltage loop pi regulator allocating time 200us, requires middle dc voltage maximum fluctuation to be no more than 3% of rated voltage, that is:

$\frac{1}{2}{C}_{\mathrm{dc}}{(U_{\mathrm{dc}}+\mathrm{\&Delta;U})}^2-\frac{1}{2}{C}_{\mathrm{dc}}{U}_{\mathrm{dc}}^2\&GreaterEqual;\mathrm{\&Delta;P}\&times;t$

Wherein: Δ U is the maximum fluctuation of the middle dc voltage of permission;

Δ P is the power of load variations;

T is pi regulator allocating time;

According to heating situation and the life-span of above-mentioned two formula and electric capacity, consider that certain allowance chooses capacitance simultaneously.

For this project, have according to above-mentioned first formula:

$C_{\mathrm{dc}}\&GreaterEqual;\frac{0.55I_s}{2\mathrm{\&pi;}\&times;0.01U_{\mathrm{dc}}\&times;f_{\mathrm{sw}}}=0.3\mathrm{mF}$

According to second formula, change 50% suddenly according to load, DC bus fluctuation is less than 15%, according to design above, P is 100kW, and Δ P is 100kWX50%=50kW, and t generally gets 20 switch periods, switching frequency is got 8kHz, and so, calculating gained DC side Support Capacitor is:

$C_{\mathrm{dc}}\&GreaterEqual;\frac{2\&times;\mathrm{\&Delta;P}\&times;t}{{(U_{\mathrm{dc}}+\mathrm{\&Delta;U})}^2-{U_{\mathrm{dc}}}^2}=2.225\mathrm{mF}$

Consider certain allowance, choosing DC side Support Capacitor is 2.5mF.

Pre-charge circuit is in parallel with filter capacitor, major function be to reduce the impulse current to input capacitance while starting.In the time that PCS starts, if there is no the direct closed main contactor of pre-charge circuit, cell voltage can directly be added on filter capacitor, and filter capacitor initial voltage is 0V, according to I=c*du/dt, can know that the temporary impact electric current producing on electric capacity will be very large, even exceed the restriction of the du/dt of capacitor permission, can affect the useful life of capacitor.So conventionally design a pre-charge circuit, after pre-charge resistance current limliting, then give capacitor charging, in the time that capacitance voltage approaches external voltage, then pre-charge circuit is disconnected.Therefore, the effect of the restricted impulse current of pre-charge circuit, protection device.

Referring to Fig. 1,2 known; the core controller of the control system of mobile energy storage PCS is connected with net side ADC module, DC side ADC module, driving and power protecting circuit; it is mainly for the control of the mobile energy-accumulating power station of 100kW, and mobile energy storage device adopts the structure access electrical network of single stage type.

Voltage acquisition unit on current acquisition unit and the electrical network of net side ADC module connection VSC current on line side collecting unit, PCS net side.VSC current on line side collecting unit is arranged on net side filter and VSC(Voltage Source Converter; Voltage source converter) between output, for gathering the current signal of inverter output; The break-make of grid-connected switch control output circuit, and by core controller control; Voltage acquisition unit on electrical network is arranged on grid-connected switch and electrical network PCC point, gathers the voltage signal of electrical network.

DC side ADC module connects DC capacitor voltage collecting unit, DC bus current collecting unit, capacitance voltage collecting unit is arranged on electric capacity, for gathering capacitance voltage, DC bus current collecting unit is arranged on DC bus, for gathering DC bus current; Switch is PCS DC side on-off element, is arranged between precharge cell and energy storage device battery pack, and by core controller control break-make; DC side power supply collecting unit is arranged between precharge cell and VSC DC side, gathers PCS DC voltage signal.

Drive and power protecting circuit connection VSC, core controller output drive signal, to driving and power protecting circuit, is controlled discharging and recharging of battery pack.Core controller is through CAN connected system transmission monitor, the energy storage station EMS system that system transmission monitor is movable energy storage system.

Known referring to Fig. 2, core controller comprises fpga chip, DSP, RS232 interface, power circuit and real-time ethernet interface, and RS232 interface connects input equipment.DSP is mainly responsible for real-time operation processing and Communication Control, real-time operation processing relates to that digital filtering, static coordinate conversion, rotating coordinate transformation, digital PLL algorithm, PI regulate and SVPWM generates the realization of the control algolithms such as duty ratio, and Communication Control relates to master control, BMS etc. and communicating.

FPGA by gather data upload in DSP, for the processing of control algolithm; DSP carries out control algolithm, and generates under duty cycle information and pass in FPGA, compares output PWM control impuls with the triangular carrier in FPGA.The access port of fpga chip has analog signal sampling modulate circuit, switching value optocoupler input interface circuit, switching value optocoupler output interface circuit, PWM optical fiber to drive interface circuit and IPM fault optical fiber input interface circuit.

Generally all belong to the forceful electric power signal of high voltage, large electric current from current transformer signal out, the level of its switching value control and status signal is generally also at least DC24V, and enter controller or be generally weak electric signal from the signal of controller output, therefore need to design the interface circuit of current transformer to controller, current transformer high voltage, large current signal is out converted to the low-voltage, the little current signal that are applicable to controller.In field of power electronics, forceful electric power to the interface circuit of light current except completing high voltage signal to the translation function of low voltage signal, also need to realize the isolation on electric, forceful electric power and light current are realized the thorough isolation on electric, to improve the antijamming capability of system.The isolation of analog signal generally all adopts Hall element, instrument transformer or linear optical coupling to realize; The isolation of switching value signal generally all adopts optocoupler to realize isolation; The isolation of pwm signal can adopt high speed photo coupling isolation, also can adopt optical fiber isolation.

The controller of PCS carries out computing by CPU and realizes various control functions, specific as follows:

(1) precharge

While use for the first time behind Mobile energy storage system arrival destination, need to carry out precharge, charge to DC bus capacitor by the pre-charge circuit of major loop on the one hand, make it to reach scheduled voltage, on the other hand to batteries charging, make it to meet application requirements.

(2) grid-connected charging control

And net state under, PCS can realize net side direction energy-storage system and carry required energy, charging current, charge power are controlled, and harmonic content is controlled in rated range.

(3) grid-connected control of discharge

And net state under, PCS can realize energy-storage system and carry required energy to net side, charging current, charge power are controlled, and harmonic content is controlled in rated range.

(4) net side power factor controlling

And net state under, PCS can regulate net side power factor, make energy-storage system discharge or absorbing reactive power.

(5) the grid-connected net that leaves

PCS can make energy-storage system depart from security and stability electrical network, is from net state by grid-connected state-transition.

(6) turn grid-connected from net

PCS can make energy-storage system access with security and stability electrical network, by changing into from net state and net state.

Switch element and grid-connected switch adopt IGBT, adopt the 2MBI600VN of Fuji ?120 ?50 model IGBT.Each IGBT withstand voltage 1200V, maximum permission direct current is 600A.The driving of IGBT can be selected discrete device or Intelligent Power Module (IPM, Intelligent Power Module), and connect the controller of PCS by driving, if need specialized designs drive circuit while selecting discrete device, select to drive chip, general driving comprises 4 parts:

(1) power supply conversion portion

Power supply conversion portion, by the 15V power supply of input, through two Switching Power Supplies, is converted to the 15V power supply of 2 tunnel isolation, supplies with respectively and manages up and down IGBT use.

(2) optical fiber conversion portion

The fiber pulse signal that optical fiber conversion portion is sent control system here, is converted to the signal of telecommunication; Meanwhile, the driving guard signal that drive circuit is produced, is converted to light signal, delivers to control system.

(3) drive part

Drive part provides forward, reverse current, to IGBT gate pole capacitor charge and discharge, thereby opens, turn-offs IGBT, and driving maximum output current is 20A.Open and turn-off the different resistances of employing, pass resistance break is greater than opens resistance, to reduce shutoff voltage pulse.Drive part adopts the special driving chip 2SP0115T2Ax-2MBI600VN-120-50 of CONCEPT company.

(4) monitor protection part

Generally can realize power supply power-fail detection, short circuit (overcurrent) protection, the protection of overvoltage active clamper etc.

By reference to the accompanying drawings the utility model is exemplarily described above; obviously the utility model specific implementation is not subject to the restrictions described above; as long as adopted the improvement of the various unsubstantialities that method of the present utility model design and technical scheme carry out; or without improving, design of the present utility model and technical scheme are directly applied to other occasion, all within protection range of the present utility model.

Claims (8)

1. move the power conversion system of energy storage, comprise main circuit and controller, it is characterized in that: the DC bus of described main circuit connects battery pack and is connected to voltage source converter through switch element, filter capacitor, described voltage source converter is connected to electrical network through net side filter, grid-connected switch, and described filter capacitor is parallel with pre-charge circuit;

Described controller comprises core controller; and the net side ADC module, DC side ADC module, driving and the power protecting circuit that are connected with core controller; described net side ADC module connects the grid-connected switch of VSC current on line side collecting unit, PCS net side; and voltage acquisition unit on electrical network; described DC side ADC module connects DC capacitor voltage collecting unit, DC bus current collecting unit.

2. the power conversion system of mobile energy storage according to claim 1, it is characterized in that: described net side filter is to be by two inductance and a LCL filter that electric capacity forms, L is current transformer side inductance value value 145-155 μ H, LS is net side inductance value value 295-305 μ H, electric capacity value 6.2-6.5 μ F.

3. the power conversion system of mobile energy storage according to claim 1, is characterized in that: described filter capacitor $C_{\mathrm{dc}}\&GreaterEqual;\frac{2\&times;\mathrm{\&Delta;P}\&times;t}{{(U_{\mathrm{dc}}+\mathrm{\&Delta;U})}^2-{U_{\mathrm{dc}}}^2}=2.225\mathrm{mF};$

Wherein: P is 100kW, Δ P is 100kWX50%=50kW, and t gets 20 switch periods, and switching frequency is got 8kHz.

4. the power conversion system of mobile energy storage according to claim 3, is characterized in that: described filter capacitor value 2.5mF.

5. the power conversion system of mobile energy storage according to claim 1, it is characterized in that: described switch element and grid-connected switch adopt IGBT, each described IGBT adopt model be the 2MBI600VN of Fuji ?120 ?50, its withstand voltage is 1200V, it is maximum that to allow direct current be 600A.

6. the power conversion system of mobile energy storage according to claim 1, is characterized in that: described core controller is through CAN connected system transmission monitor.

7. the power conversion system of mobile energy storage according to claim 6, is characterized in that: described core controller comprises fpga chip, DSP, power circuit and real-time ethernet interface.

8. the power conversion system of mobile energy storage according to claim 7, is characterized in that: described core controller is also provided with RS232 interface, and connects input equipment by RS232 interface.

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