CN203871869U - Device storing energy on basis of flywheel and inhabiting power fluctuations of wind turbine generator set - Google Patents

Abstract

The utility model provides a method and a device storing energy on the basis of a flywheel and inhabiting power fluctuations of a wind turbine generator set. The device storing energy on the basis of the flywheel and inhabiting the power fluctuations of the wind turbine generator set enables a flywheel energy storage device to be accessed to a power output point of the wind turbine generator set; and, through adjustments of a flywheel angular velocity of a flywheel energy storage system, and through adjustments of outlet power of the wind turbine generator set by utilizing a momentum increment of the flywheel energy storage device, peak load shifting and power smoothing are performed, and outlet voltage is stabilized.

Description

The device of the inhibition wind-powered electricity generation unit power fluctuation based on flywheel energy storage

Technical field: the utility model relates to a kind of method and device of the inhibition wind-powered electricity generation unit power fluctuation based on flywheel energy storage.Belong to energy storage control field.Be used for solving wind-powered electricity generation unit output-power fluctuation problem.

Background technology: wind power generation development at present rapidly, become the important component part of electric power system, but due to the fluctuation of wind-powered electricity generation own and randomness, more and more become the obstacle of restriction new forms of energy development, along with the continuation expansion of generation of electricity by new energy scale, it is particularly urgent that this problem seems.Energy storage fundamentally solves the effective way of wind power generation access problem just, makes up intermittence and the unsteadiness defect of wind-powered electricity generation by energy-storage system, thereby realize power, is smoothly connected to the grid.Stablizing of wind-powered electricity generation also shows stablizing and frequency stability of Power Output for Wind Power Field in addition, and the research of this respect problem at present mainly concentrates on and utilizes energy-storage system to stabilize wind power output power frequency fluctuation.According to present scholar's a lot of theories and experimental study, energy-storage system can effectively improve wind power system frequency stability really, and energy storage system capacity is larger, the faster effect of response speed is better.

Flywheel energy storage system has quick absorption or discharges the feature of meritorious and reactive power, to improving the power-balance situation of system, the fluctuation that reduces the voltage fluctuation of grid-connected place wind-powered electricity generation and stabilize wind energy turbine set output has good effect, can also play the effect that strengthens system run all right simultaneously.The stability that strengthens wind-electricity integration system just needs energy-storage system to have the ability of quick response, because each parameter of system changes very fast in transient process, flywheel energy storage mode response speed can reach 1-20ms, can compensate fast unbalanced power amount, gain merit fast and between system, reactive power exchange, with this, effectively improve voltage fluctuation, as voltage dip, wave distortion and flickering etc.

The wind-powered electricity generation of random fluctuation accesses electrical network as power supply, by causing the reserve capacity of original system to increase, even also needs optional equipment balance and stability device, and the system performance driving economy of making decreases.

Utility model content:

Utility model object: method and the device of the inhibition wind-powered electricity generation unit power fluctuation based on flywheel energy storage, its objective is the wind-powered electricity generation unit output-power fluctuation problem that solves.

Technical scheme: the utility model is achieved through the following technical solutions:

The method of the inhibition wind-powered electricity generation unit power fluctuation based on flywheel energy storage, it is characterized in that: this method accesses energy accumulation device for fly wheel the power stage point of wind-powered electricity generation unit, by regulating the flywheel angular speed of flywheel energy storage system, utilize the power of the momentum increment compensation wind-powered electricity generation machine set outlet of energy accumulation device for fly wheel, make the power output of unit press close to reference value, reach the peak load that disappears, power smoothly and the object of stabilization of export voltage.

Described wind-powered electricity generation unit power output reference value adopts the method based on low-pass first order filter to determine, by actual Power Output for Wind Power Field curve negotiating filter, the part of rapid fluctuations in curve is filtered, obtain a comparatively level and smooth curve, as wind energy turbine set desired output power curve;

Control strategy based on low-pass first order filter is to be by the power designs of injecting electrical network in formula f _ccut-off frequency for filter; Flywheel energy storage system discharges and recharges reference power and is

$P_{\mathrm{ref}}=\frac{\mathrm{Ts}}{1+\mathrm{Ts}}{P}_w$

Now, after stabilizing, injects overpower the rate of change of power and the smoothness of power of electrical network all relevant with time constant T; The value of T is larger, and the power variation rate of injecting electrical network is less, and the power of output is also just more level and smooth.

Flywheel angular speed adopts fuzzy self-adaption to become the filter control method of time constant, be specially: on the basis of conventional lowpass filter, consider the overload situations of flywheel, when required power surpasses the ceiling capacity that flywheel energy storage system can store and discharge, by regulating time constant, the overload of fly wheel system and stablizing of current transformer direct voltage have been controlled, after the filter that becomes time constant, add a fuzzy adjustment amount, make Speed of Reaction Wheels return to zone of reasonableness, extended the life-span of energy-storage system.

The filter control method of fuzzy self-adaption change time constant is as follows:

The power that wind energy turbine set is sent is Pw, through after traditional low pass filter, calculates Pg, and releases P thus _ref; The operating state P of judgement flywheel energy storage system _refwhether transfinite, i.e. the following formula of the size of γ (t), and execution:

Work as ω _max>=ω>=0.9 ω _maxtime, now flywheel energy storage system, in higher energy storage state, charges when should allow flywheel energy storage system charging less, in the time of electric discharge, discharges more, and given power deducts an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness;

Work as ω _min≤ ω≤1.1 ω _mintime, now flywheel energy storage system, in compared with low discharge state, charges when should allow flywheel energy storage system charging more, in the time of electric discharge, discharges less, and given power adds an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness; Last set-point adds that adjusted value has drawn the flywheel power given value that we are final $P_{\mathrm{ref}}^{\mathrm{final}}=P_F^{\mathrm{ref}}+\mathrm{\Δ}=P_F^{\mathrm{ref}}+\mathrm{\ΔP}*P_{\mathrm{rate}}.$

The job step of the control of fuzzy self-adaption is as follows:

(1) power that wind energy turbine set is sent is Pw, through after traditional low pass filter, calculates Pg, and releases P thus _ref;

(2) operating state of judgement flywheel energy storage system

P _refwhether transfinite, i.e. the size of γ (t), and carry out following formula:

Wherein, α in formula _fUUZY=f _fUZZY(δ (t)), its fuzzy reasoning table is as shown in table 1, fuzzy domain be 1.5 ,-1,0,1,1.5}, fuzzy language variable is { NB, NS, ZO, PS, PB};

Table 1 is adjusted the fuzzy reasoning table of time constant

(3) carry out time, the rotational speed omega state of judgement flywheel energy storage system

Work as ω _max>=ω>=0.9 ω _maxtime, now flywheel energy storage system, in higher energy storage state, charges when should allow flywheel energy storage system charging less, in the time of electric discharge, discharges more, and given power deducts an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness;

Work as ω _min≤ ω≤1.1 ω _mintime, now flywheel energy storage system, in compared with low discharge state, charges when should allow flywheel energy storage system charging more, in the time of electric discharge, discharges less, and given power adds an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness;

The fuzzy control rule of Δ P value is as shown in table 2, fuzzy domain be 1 ,-0.8 ,-0.2,0,0.2,0.8,1}, fuzzy language variable is { NB, NM, NS, ZO, PS, PM, PB}.

Table 2 is adjusted the fuzzy reasoning table of the rotational speed omega of flywheel

(4) the given power that finally draws fly wheel system is:

$P_{\mathrm{ref}}^{\mathrm{final}}=P_F^{\mathrm{ref}}+\mathrm{\Δ}=P_F^{\mathrm{ref}}+\mathrm{\ΔP}*P_{\mathrm{rate}}$

Step (1) has drawn the initial set-point of flywheel energy storage system, and the time constant of low pass filter is chosen the effect that will be stabilized by us and determined, time constant T is larger, and smooth effect is better, and the flywheel energy storage system capacity needing is also just larger.The P drawing thus _refthe rated power that may exceed flywheel;

In step (2), adopt the filter that becomes time constant, its time constant is by P _refdetermine, work as P _refwhile surpassing set point, utilize fuzzy self-adaption principle to adjust its time constant, make P _refwithin reverting to setting range; The long work of flywheel energy storage system may make its rotating speed state in higher or lower level, and now the control strategy of energy-storage system just must be considered self rotating speed state of flywheel, to reach the object that maintains DC bus-bar voltage;

In step (3), when the rotational speed omega of flywheel is during in higher level, on the basis of power given value, deduct a fuzzy adjustment value; When the rotational speed omega of flywheel is during in reduced levels, on the basis of power given value, add an adjusted value;

The set-point of final step (4) adds that adjusted value has drawn the flywheel power given value that we are final

The control system outer shroud of flywheel energy storage system adopts active power ring, to realize the level and smooth control of wind-powered electricity generation unit active power of output; Interior ring is electric current loop, is that d, the q shaft current that regulates motor followed the tracks of set point.

A kind of inhibition wind-powered electricity generation unit power fluctuation device based on flywheel energy storage of implementing the method for the above-mentioned inhibition wind-powered electricity generation unit power fluctuation based on flywheel energy storage, it is characterized in that: this device comprises motor side current transformer and grid side current transformer, motor side current transformer is connected with grid side current transformer, motor side current transformer is connected to wind wheel by generator, and grid side current transformer is connected with electrical network by step-up transformer; On the power stage point between motor side current transformer and grid side current transformer, be connected to energy accumulation device for fly wheel.

Energy accumulation device for fly wheel comprises two-way PWM current transformer, moving/to send out all-in-one and flywheel rotating disk, and two-way PWM current transformer is connected to the power stage point between motor side current transformer and grid side current transformer, and two-way PWM current transformer is connected to flywheel by a moving/all-in-one.

Advantage and effect: the utility model provides a kind of method and device of the inhibition wind-powered electricity generation unit power fluctuation based on flywheel energy storage, it accesses energy accumulation device for fly wheel the power stage point of wind-powered electricity generation unit, by regulating the flywheel angular speed of flywheel energy storage system, utilize the power of the momentum incremental adjustments wind-powered electricity generation machine set outlet of energy accumulation device for fly wheel, disappear peak load, power is level and smooth, stabilization of export voltage.

In wind-powered electricity generation unit grid-connected system, apply flywheel energy storage system and can access the alleviation in very large degree, thereby realize the object of electrical network and wind energy turbine set doulbe-sides' victory.In addition, under Power Market now, wind-powered electricity generation is faced with the problems such as cost is higher, power supply quality is not high, the power that constitutes competition is poor, adopts flywheel energy storage system to coordinate wind energy turbine set operation, and it is a good approach that effective solution alleviation is realized to wind-powered electricity generation maximizing the benefits.

The utility model is to utilize flywheel energy storage system to strengthen wind-powered electricity generation stability, reduce the power fluctuation at wind-powered electricity generation set grid-connection place and then stabilize the fluctuation that wind energy turbine set is exported, and can also play the effect that strengthens system run all right simultaneously.Improve wind energy turbine set power supply quality, improve wind-powered electricity generation economy.

Accompanying drawing explanation:

Fig. 1 is composition and the system configuration of wind-powered electricity generation unit unit flywheel energy storage system;

Fig. 2 is flywheel energy storage composition of the control system and system configuration;

Fig. 3 is the control principle drawing of fuzzy adaptive filter.

Embodiment: the utility model is described further below in conjunction with accompanying drawing:

The utility model provides a kind of method of the inhibition wind-powered electricity generation unit power fluctuation based on flywheel energy storage, this method accesses energy accumulation device for fly wheel the power stage point of wind-powered electricity generation unit, by regulating the flywheel angular speed of flywheel energy storage system, utilize the power of the momentum increment compensation wind-powered electricity generation machine set outlet of energy accumulation device for fly wheel, make the power output of unit press close to reference value, reach the peak load that disappears, power smoothly and the object of stabilization of export voltage.

Described wind-powered electricity generation unit power output reference value adopts the method based on low-pass first order filter to determine, by actual Power Output for Wind Power Field curve negotiating filter, the part of rapid fluctuations in curve is filtered, obtain a comparatively level and smooth curve, as wind energy turbine set desired output power curve;

Control strategy based on low-pass first order filter is to be by the power designs of injecting electrical network in formula f _ccut-off frequency for filter; Flywheel energy storage system discharges and recharges reference power and is $P_{\mathrm{ref}}=\frac{\mathrm{Ts}}{1+\mathrm{Ts}}{P}_w$

Now, after stabilizing, injects overpower the rate of change of power and the smoothness of power of electrical network all relevant with time constant T; The value of T is larger, and the power variation rate of injecting electrical network is less, and the power of output is also just more level and smooth.

Flywheel angular speed adopts fuzzy self-adaption to become the filter control method of time constant, be specially: on the basis of conventional lowpass filter, consider the overload situations of flywheel, when required power surpasses the ceiling capacity that flywheel energy storage system can store and discharge, by regulating time constant, the overload of fly wheel system and stablizing of current transformer direct voltage have been controlled, after the filter that becomes time constant, add a fuzzy adjustment amount, make Speed of Reaction Wheels return to zone of reasonableness, extended the life-span of energy-storage system.

The feature of wind power generation maximum is exactly meritorious intermittence and the randomness presenting along with the variation of wind speed of its output.The change at random of wind speed not only scope is large, and pace of change is fast.By flywheel applications, in wind power system, be exactly the capability of fast response that makes full use of flywheel energy storage system, can absorb fast or send meritorious and reactive power, effectively responded the demand of system, maintain the stable of voltage and frequency.

The target of flywheel energy storage system is the power fluctuation of mild wind-powered electricity generation unit, and according to mains frequency fluctuation situation, absorbs or exports certain power.Therefore no matter be that the control target of flywheel energy storage system is the reference power P that will make its output tracking wind turbine group system at charging or discharge regime _ref.

For the flywheel energy storage system that will participate in power back-off control, its reference power is comprised of two parts: the actual value of the meritorious output of wind energy turbine set and the power deviation between desired value.This part reference power is in order to the meritorious output of mild wind energy turbine set.When the actual output of wind energy turbine set is during lower than desired value, reference power is for negative, and flywheel energy storage system discharges corresponding energy with the output of compensation wind energy turbine set.When wind energy turbine set output, reference power is for just during higher than desired value, and flywheel energy storage system gets up unnecessary energy storage by accelerator.

When wind energy turbine set power is during in crest, flywheel accelerates rotation, and the form by crest energy with mechanical energy stores, to can discharge during in trough at wind energy turbine set power.Theoretically, before Speed of Reaction Wheels does not arrive the upper limit that mechanical structure determines, it just can one straight through the conversion of accelerating to carry out energy.For steady Power Output for Wind Power Field, before not reaching the upper limit, Speed of Reaction Wheels must change by real-time tracking power.And therefore square being directly proportional of the kinetic energy that rotating object has and its rotating speed can treat that storage power determines and expect rotating speed with the relation of Speed of Reaction Wheels variation by foundations.

In system, the highest and minimum speed of establishing flywheel is respectively ω max and ω min, and the ceiling capacity that flywheel energy storage system can store and discharge is:

$E_{\max }=\frac{1}{2}{{\mathrm{J\ω}}_{\max }}^2-\frac{1}{2}{{\mathrm{J\ω}}_{\min }}^2$

The power that wind energy turbine set is injected electrical network in the situation that there is no flywheel energy storage system is Pw, and after adding flywheel energy storage system, the power of wind energy turbine set injection electrical network becomes P _g, the power of handling up of energy-storage system is Pref, the relational expression between them is:

Pw=P _g+P _ref

To above formula integration, try to achieve the expectation energy of flywheel rotor:

$E_{\mathrm{ref}}=E_{\mathrm{to}}+\underset{t0}{\overset{t1}{\∫}}{P}_{\mathrm{ref}}\mathrm{dt}$

In formula, E _refinitial mechanical energy for flywheel rotor.By the relation of rotating speed and energy, just can try to achieve expectation rotating speed is again:

${\mathrm{\ω}}_{\mathrm{ref}}=\sqrt{{2E}_{\mathrm{ref}}/J}$

ω _reffor flywheel angular speed, the moment of inertia that J is flywheel.

Though the control strategy of conventional lowpass filter can be stabilized the power fluctuation of wind energy turbine set, based on this control strategy, cannot effectively regulate the rotating speed state of flywheel, and surpass when specified when required power, cannot be to its tuning.Its control strategy is to utilize filter: the Power Output for Wind Power Field curve negotiating filter by actual, the part of rapid fluctuations in curve is filtered, and obtain a comparatively level and smooth curve, as wind energy turbine set desired output power curve.

Control strategy based on low-pass first order filter by the power designs of injecting electrical network is in formula f _ccut-off frequency for filter.

Flywheel energy storage system discharges and recharges reference power and is

$P_{\mathrm{ref}}=\frac{\mathrm{Ts}}{1+\mathrm{Ts}}{P}_w$

Now, after stabilizing, injects overpower the rate of change of power and the smoothness of power of electrical network all relevant with time constant T.The value of T is larger, and the power variation rate of injecting electrical network is less, and the power of output is also just more level and smooth.

The utility model is on the basis of conventional lowpass filter, consider the overload situations of flywheel, when required power surpasses the ceiling capacity that flywheel energy storage system can store and discharge, by regulating time constant, the overload of fly wheel system and stablizing of current transformer direct voltage have been controlled, after the filter that becomes time constant, add a fuzzy adjustment amount, make Speed of Reaction Wheels return to zone of reasonableness, extended the life-span of energy-storage system.

The filter control method of fuzzy self-adaption change time constant is as follows:

The power that wind energy turbine set is sent is Pw, through after traditional low pass filter, calculates Pg, and releases P thus _ref; The operating state P of judgement flywheel energy storage system _refwhether transfinite, i.e. the following formula of the size of γ (t), and execution:

Work as ω _max>=ω>=0.9 ω _maxtime, now flywheel energy storage system, in higher energy storage state, charges when should allow flywheel energy storage system charging less, in the time of electric discharge, discharges more, and given power deducts an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness;

Work as ω _min≤ ω≤1.1 ω _mintime, now flywheel energy storage system, in compared with low discharge state, charges when should allow flywheel energy storage system charging more, in the time of electric discharge, discharges less, and given power adds an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness; Last set-point adds that adjusted value has drawn the flywheel power given value that we are final $P_{\mathrm{ref}}^{\mathrm{final}}=P_F^{\mathrm{ref}}+\mathrm{\Δ}=P_F^{\mathrm{ref}}+\mathrm{\ΔP}*P_{\mathrm{rate}}.$

The concrete steps that fuzzy self-adaption is controlled:

(1) power that wind energy turbine set is sent is Pw, through after traditional low pass filter, calculates Pg, and releases P thus _ref;

(2) operating state of judgement flywheel energy storage system

P _refwhether transfinite, i.e. the size of γ (t), and carry out following formula:

Wherein, α in formula _fUUZY=f _fUZZY(δ (t)), its fuzzy reasoning table is as shown in table 1, fuzzy domain be 1.5 ,-1,0,1,1.5}, fuzzy language variable is { NB, NS, ZO, PS, PB};

Table 1 is adjusted the fuzzy reasoning table of time constant

(3) carry out time, the rotational speed omega state of judgement flywheel energy storage system

Work as ω _max>=ω>=0.9 ω _maxtime, now flywheel energy storage system, in higher energy storage state, charges when should allow flywheel energy storage system charging less, in the time of electric discharge, discharges more, and given power deducts an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness;

Work as ω _min≤ ω≤1.1 ω _mintime, now flywheel energy storage system, in compared with low discharge state, charges when should allow flywheel energy storage system charging more, in the time of electric discharge, discharges less, and given power adds an adjusted value make within the rotational speed omega of flywheel returns to zone of reasonableness;

The fuzzy control rule of Δ P value is as shown in table 2, fuzzy domain be 1 ,-0.8 ,-0.2,0,0.2,0.8,1}, fuzzy language variable is { NB, NM, NS, ZO, PS, PM, PB}.

Table 2 is adjusted the fuzzy reasoning table of the rotational speed omega of flywheel

(4) the given power that finally draws fly wheel system is:

$P_{\mathrm{ref}}^{\mathrm{final}}=P_F^{\mathrm{ref}}+\mathrm{\Δ}=P_F^{\mathrm{ref}}+\mathrm{\ΔP}*P_{\mathrm{rate}}$

In above step:

Step (1) has drawn the initial set-point of flywheel energy storage system, and the time constant of low pass filter is chosen the effect that will be stabilized by us and determined, time constant T is larger, and smooth effect is better, and the flywheel energy storage system capacity needing is also just larger.The P drawing thus _refthe rated power that may exceed flywheel;

In step (2), adopt the filter that becomes time constant, its time constant is by P _refdetermine, work as P _refwhile surpassing set point, utilize fuzzy self-adaption principle to adjust its time constant, make P _refwithin reverting to setting range; The long work of flywheel energy storage system may make its rotating speed state in higher or lower level, and now the control strategy of energy-storage system just must be considered self rotating speed state of flywheel, to reach the object that maintains DC bus-bar voltage;

In step (3), when the rotational speed omega of flywheel is during in higher level, on the basis of power given value, deduct a fuzzy adjustment value; When the rotational speed omega of flywheel is during in reduced levels, on the basis of power given value, add an adjusted value;

The set-point of final step (4) adds that adjusted value has drawn the flywheel power given value that we are final

The control system outer shroud of flywheel energy storage system adopts active power ring, to realize the level and smooth control of wind-powered electricity generation unit active power of output; Interior ring is electric current loop, is that d, the q shaft current that regulates motor followed the tracks of set point.

As shown in Figure 1, this device comprises motor side current transformer and grid side current transformer, and motor side current transformer is connected with grid side current transformer, and motor side current transformer is connected to wind wheel by generator, and grid side current transformer is connected with electrical network by step-up transformer; On the power stage point between motor side current transformer and grid side current transformer, be connected to energy accumulation device for fly wheel.

Wind-powered electricity generation unit unit flywheel storage system does not indicate in the location drawing of this capacitor C of DC bus capacitor C(! ), inverter is the compositions such as two-way PWM current transformer, freewheel unit.Wherein, freewheel unit comprise drive permagnetic synchronous motor moving/send out all-in-one (PMSM), flywheel rotating disk and bearings system etc., freewheel unit is positioned in airtight vacuum sleeve, the windage loss when reducing flywheel rotating disk High Rotation Speed.Two-way PWM current transformer is connected to the power stage point between motor side current transformer and grid side current transformer, and two-way PWM current transformer is connected to flywheel rotating disk by a moving/all-in-one.

Flywheel energy storage system is when charge operation state, and the drive motors of Driven by inverter freewheel unit, drags flywheel rotating disk High Rotation Speed, and electric energy conversion is mechanical energy; Flywheel energy storage system is when discharge condition, and inverter is realized freewheel unit to the energy feedback of DC side, and the mechanical energy being stored in flywheel is converted to electric energy output.

Current transformer is the PWM high-frequency current transformer that an energy can two-way conveying.Its major function is to realize the two-way conveying of energy and the frequency control of flying wheel battery, and when Fly wheel energy storage system absorbs energy from system, it is transformed into AC power by DC power supply and offers flying wheel battery in inverter mode; Otherwise the AC power that the generator in generating state is sent is rectified into DC power supply and compensates to system.

Fig. 2 is the control block diagram of flywheel energy storage system.Control system outer shroud adopts active power ring, and object is to realize the level and smooth control of wind-powered electricity generation unit active power of output; Interior ring is electric current loop, and object is that the d, the q shaft current that regulate motor are followed the tracks of set point.

Fig. 3 is the control principle drawing of fuzzy adaptive filter, in figure by U _d, I _d, ω _t-1draw t ω constantly _t.Fuzzy Calculation device 1 is used for regulating flywheel power, prevents from surpassing rated power, be by self adaptation regulates time constant T _fUUZY.Fuzzy Calculation device 2 is used for regulating flywheel state, is input as ω _twith be output as Δ P.

Claims (1)

1. the inhibition wind-powered electricity generation unit power fluctuation device based on flywheel energy storage, it is characterized in that: this device comprises motor side current transformer and grid side current transformer, motor side current transformer is connected with grid side current transformer, motor side current transformer is connected to wind wheel by generator, and grid side current transformer is connected with electrical network by step-up transformer; On the power stage point between motor side current transformer and grid side current transformer, be connected to energy accumulation device for fly wheel;

Energy accumulation device for fly wheel comprises two-way PWM current transformer, moving/to send out all-in-one and flywheel rotating disk, and two-way PWM current transformer is connected to the power stage point between motor side current transformer and grid side current transformer, and two-way PWM current transformer is connected to flywheel by a moving/all-in-one.