Fast bus transfer method and device Technical Field

The present invention relates to a fast bus transfer method, and especially, to a real-time fast transfer method. The present invention also relates to a fast bus transfer de ^¬ vice, and especially, to a real-time fast transfer device.

Background Art

Fast bus transfer (FBT) can quickly transfer a bus connected to a load (for example, a motor) to a backup power supply when a main power supply fails, and its function is not only to maintain the continuous operation of the equip ^¬ ment, but also to avoid damage to the motor or other con ^¬ nected loads. Usually, such fast bus transfer is manually started, or in the case of failure, it is started by an ex ^¬ ternal device, and its conventional transfer modes comprise three types: fast transfer, in-phase transfer, and residual voltage transfer. Each transfer mode is aimed at a particular situation, and the transfer modes each have their own criteria. Since fast transfer can theoretically keep the power interruption of the bus within the shortest time period and protect the motor or other loads from excessive or accumu ^¬ lated stress, fast transfer is usually preferred. If the criterion for fast transfer fails to be met, then the fast transfer equipment cannot send out a close command to the circuit breaker of the backup power supply, and the in-phase transfer mode will be subsequently started, that is, the in- phase transfer mode serves as a backup solution to the fast transfer mode. Likewise, the residual voltage transfer mode serves as a backup solution to the in-phase transfer mode. The criteria for these three different transfer modes are as follows:

1) Criteria for fast transfer: Αφ < (p _FTparameter and

^ FTparameter ^* Here, Αφ is the phase angle difference between the at ^¬ tenuated bus voltage and the backup power supply voltage, Af is the frequency difference between the attenuated bus volt ^¬ age and the backup power supply voltage, A(p _FTparameter is a limit parameter of Αφ , Af _FTparameter is a limit parameter of Af , in which Αφ and Af are real-time measurement values, while

(P _F T _P ara _m e _t er ^{a n d} FT _P ara _m e _t er ^are instantaneous values when the cir- cuit breaker of the main power supply opens and are deter ^¬ mined by the user.

2) Criterion for in-phase transfer: A#? _orecaji < 10°.

Here, A(p _forecast is a forecast phase angle difference between the attenuated bus voltage and the voltage of the backup po ^¬ wer supply, Aq) _forecast being a forecast value. If the fast trans ^¬ fer is missed, then the fast bus transfer device will auto ^¬ matically convert to the in-phase transfer. In-phase transfer is suitable for the situation where the phase angle differ ^¬ ence is zero at the moment when the circuit breaker of the backup power supply is closed.

3) Criterion for residual voltage transfer: when the bus voltage drops to a predefined value, for example 30% of the rated value, then close the circuit breaker of the backup power supply.

This transfer is the slowest of all the transfer modes.

The criteria for the above various transfer modes are all restricted by the characteristics of the motor or other loads. The terminal voltage of the motor caused by the volt ^¬ age difference across the circuit breaker should not exceed a permitted over-voltage value. It is usually 1.1 times the rated voltage U _n . Fig. 1 shows the characteristic an attenu ^¬ ated residual voltage, in which are illustratively shown a fast transfer section 30, an in-phase transfer section 20 and the voltage ^u of the backup power supply. Supposing that the voltage difference is 1.0 U , on the right side of the curve A' -A' ' is a safe area for re-supply. When the voltage differ ^¬ ence is lower than 1.0 U _n , a new voltage level will form a new safe area, i.e., the right side of B'-B''. Since the premise for determining parameters is to com ^¬ prehensively analyze the residual voltage characteristic, it is hard for the user to use fast transfer mode correctly. When the motor disconnects the electrical connection with the power supply, the energy stored in the magnetic field of the motor will generate an induced voltage which is referred to as residual voltage. The amplitude and frequency of this in ^¬ duced voltage will attenuate, the attenuation trend and at ^¬ tenuation rate depending upon a variety of factors, such as the type of motor, the load of the motor, the inertia of the motor and so on. Therefore, it is difficult for the user to determine the values for the parameters ^Δ ^¾™<*,· _anc j Δ/^™*, properly. At the same time, theoretically, the residual volt ^¬ age characteristic will change if any one of the factors var ^¬ ies, therefore ^FIP^^ _ancl 4 ^Ώ > ₀ ™^ _w ill also need to be re- determined accordingly, however, it is quite difficult. In view of this, the user usually determines relatively small values for _{so as to aV} oid the fast bus transfer exceeding its application range, with the result that the fast bus transfer cannot function adequately, thereby losing the best occasion for re-supplying the motor connected to the bus and maintaining operation continuity, while waiting for in-phase transfer to respond takes a time period of several hundreds of milliseconds. This delay will prolong the transfer time, and increase the impact current and impact moment.

Contents of the invention

The object of the present invention is to provide a fast bus transfer method to reduce, by transferring between a main power supply and a backup power supply, the impact on a load connected to a bus due to a power cut. The method comprises: 1) calculating the amplitude AU _foncast of the voltage vector difference between the bus and the backup power supply and calculating the phase angle difference Αφ _forecast between the bus and the backup power supply; 2) transferring the load on the bus to said backup power supply only when AU _forecast is less than its limit value AU _RTFTpammeter and Αφ _forecast is less than 90°.

According to one aspect of the present invention, both a _re forecast values at the moment when the circuit breaker of said backup power supply is closed.

According to another aspect of the present invention,

j_ _s obtained by calculation according to the following formula :

forecast ⁼ Mforecast ⁺ ^ A ^— 2 * J ^{j 1} _M f _orecast * U _A * COSA^O f^ore^cast ^ j_ _{n wh} i _ch JJ ^ Mforecast j_ _s forecast value of a motor's residuaall voltage, and

the voltage of the backup power supply.

According to yet another aspect of the present invention ^uM *** j_ _s obtained by calculation according to the following formula:

U Mforecast = U. f 1 + λ * At + {λ * AtJ

, in which is the real-time amplitude at the moment ' ² ; ^Άΐ is the time difference between the moment ^ ² and the moment , th the time period for

the circuit breaker to close; and ^τ , ^τ being a time con- stant.

According to yet another aspect of the present invention, j_ _s obtained by calculation according to the following formula :

*a*At' ^>

, in which is the phase difference at the moment ^ ² , is the angular velocity difference at the moment , and ^a is the attenuation rate of an angular velocity defined according to a residual volt- age transfer mode, and ^Δ ' is the time difference between the moment and the moment , that is, the time period for the circuit breaker to close. According to yet another aspect of the present invention, λ is obtained by calculation according to the following for-

mula: ^{2 1} , in which is the real-time amplitude at the moment .

According to yet another aspect of the present invention,

^ ^ω 'ϊ and ^a are obtained by calculation according to the fol-

Αφ - Αφ

Αω, = ^L

lowing formulae respectively: ¹ t ² - t ¹ , and

Αω h, - Δω,

^ ² , in which ^ ^ω ' ^ι is the angular velocity difference at the moment ^ ¹ , and is the phase difference at the mo- ment ¹ .

The object of the present invention is to further provide a fast bus transfer device to reduce, by transferring between a main power supply and a backup power supply, the impact on a load connected to a bus due to a power cut. The device com ^¬ prises: a detection module, for detecting signals at the main power supply, the backup power supply and the bus; a calcula ^¬ tion module, for receiving said signals, and calculating the amplitude AU _forecast of the voltage vector difference between the bus and the backup power supply and calculating the phase angle difference Aq) _forecast between the bus and the backup power supply; a comparison module, for receiving AU _forecast and

(P _f0 reca _S t > comparing A(p _forecast with its limit value AU _{RTFTparameter} , and comparing Aq) _forecast with 90°; and a transfer module, for receiv- ing the comparison results from the comparison module, and transferring the load on the bus to said backup power supply only when AU _forecast is less than its limit value AU _{RTFTparameter} and <Ρ fire** ^{l s l e S S t h a n 9 0} ° -

According to one aspect of the present invention,

calccuullaattiioonn mmoodduullee oobbttains ^ ' f° ^{re ast} by calculation according to the following formula: forecast ⁼ ^U Mforecast ^' + ¾ ^{2 ~} 2 * U Mforecast * ¾ * CO SΔ forecast

in which ^ ^M f° ^recast is a forecast value of a motor' s residual voltage, and ^ ^A is the voltage of the backup power supply.

According to another aspect of the present invention, said calculation module obtains ^ ^M f° ^recast by calculation according to the following formula:

U _Mfmt = U _t (l + A * At + * {A * Atf) _υ

^ J , in which ' is the real-time amplitude at the moment ; t j_ _s the time difference between the moment ^ ² and the moment , that is, the time period for

Λ =-Ι

the circuit breaker to close; and ^τ , ^τ being a time con ^¬ stant .

According to yet another aspect of the present invention, said calculation module obtains ^f° ^recast by calculation according to the following formula:

^ 'ffoorreeccaasstt = ^~ ΑψΨί> ₂ + ⁺ Δ ^βω λί ₂ * ^, A ^fl, t ⁺ + ^7 * O"f ** A ⁰¹ t Αφ

¹ , in which ¹ is the phase difference at the moment ^ ² , ^ ^ω Ί is the angular velocity difference at the moment ^ ² , i _s the time difference be ^¬ tween the moment ^ ² and the moment , that is, the time pe ^¬ riod for the circuit breaker to close, and ^a is the attenua ^¬ tion rate of an angular velocity defined according to a re ^¬ sidual voltage transfer mode.

According to yet another aspect of the present invention, said calculation module obtains ^ by calculation according to the following formula:

, in which ' ^ι is the real-time amplitude at the moment ¹

According to yet another aspect of the present invention, and ^a are obtained by calculation by said calculation module according to the following formulae: is the angular velocity difference at the moment , and is the phase difference at the moment .

The advantages of the present invention lie in the fol ^¬ lowing: by way of calculating a real-time residual voltage, it is unnecessary for the user to be well-acquainted with the residual voltage characteristic; he only needs to set the li- mit of the voltage difference at the moment when the circuit breaker of the backup power supply is closed, and fast trans ^¬ fer can then be easily achieved; moreover, it is unnecessary to adjust previous settings in response to variation of the residual voltage characteristic, thereby making it extremely convenient for the user to operate, and overcoming the imper ^¬ fections in the prior art.

Brief description of the accompanying drawings

The features and advantages of the present invention will become clearer in combination with the following accompanying drawings, in which identical symbols represent identical com ^¬ ponents or means:

Fig. 1 illustratively shows the characteristic of an at ^¬ tenuated residual voltage in the prior art;

Fig. 2 illustratively shows a system in which the method and device according to the present invention are used;

Fig. 3 illustratively shows a vector relationship among the amplitude ^Αυ /°™™ ^« of the voltage vector difference between the bus and the backup power supply, the phase angle differ ^¬ ence between the bus and the backup power supply, the forecast value of a motor's residual voltage, and the voltage ^u of the backup power supply; and

Fig. 4 illustratively shows the characteristic of an at ^¬ tenuated residual voltage in the present invention.

Exemplary embodiments

Fig. 2 illustratively shows a system in which the method and/or device according to the present invention are used, in which the buses BB are electrically connected to each other during normal operation and can be connected to other loads such as a motor. A main power supply MP and a backup power supply BP can be respectively connected to the buses BB through a fast bus transfer device FBT .

The fast bus transfer method according to the present in ^¬ vention reduces the impact on the load connected to the buses BB (such as an electric motor) due to a power cut by trans ^¬ ferring between the main power supply MP and the backup power supply BP, and comprises two steps:

1) calculating the amplitude AU _forecast of the voltage vec ^¬ tor difference between the bus BB and the backup power supply BP and calculating the phase angle difference Αφ _forecast between the bus BB and the backup power supply BP;

2) transferring the load on the bus to the backup power supply BP only when AU _forecast is less than its limit value

_{RTFTparameter} and A(p _forecast is less than 90°.

In this case, and are forecast values at the moment when the circuit breaker of the backup power supply BP is closed, while _anc j gQ° _are permitted values at the moment when the circuit breaker of the backup power supply BP is closed.

Fig. 3 illustratively shows a vector relationship among the amplitude ^Αϋforecas ' of the voltage vector difference, the phase angle difference ^{ψ ∞} °*< _r the forecast value ^Mforecas< of the motor's residual voltage, and the voltage ^u of the backup power supply. The voltage difference depends upon the angle difference between the residual voltage of the bus and the voltage of the backup power supply. ^Δ? /™ ^> is obtained by calculation according to the following formula (1) :

_ 2 * U _Mfamasl *U _A *COSA^ _{re∞s( W} h _lC h _ _{Q ¾} f _O re _C a _S t value of the motor' s residual voltage at the moment when the circuit breaker of the backup power supply BP is closed, and is the voltage of the backup power supply.

It can be known from the residual voltage characteristic formula U(t) = U ₀ *e ^< sm((a> ₀ - _a *t)*t _{+ l} p ₀ ) _{that the real} _ _{time amp} litude of the residual voltage at a certain moment is ^u , = ^u o* ^{e T} _r j_ _n which ^u o is the initial amplitude of the residual voltage, ^τ is a time constant of the attenuated residual voltage, ^ω ° is the initial angular velocity of the residual voltage, is the initial phase of the residual voltage, and ^a is the at ^¬ tenuation rate of the angular velocity. In view of the fact that both and ^e are constants, the amplitude ^u > at any mo ^¬ ment * can be obtained by calculation as long as the value of the time constant ^τ is known. This can be achieved using the following algorithm, for example, if the amplitude at the

_A

moment is^-^ ^0*6 and the amplitude at the moment is

— ^L - e ^τ

u ^> ₁ = ^u * ^{e T} _/ then ^U ' is obtained, and this is expanded using u,, _ _l _t _l t _i+ i ft.- ¹ 1

Taylor's formula to : ^u '> ^{T 1 τ )} _} i _et λ can be obtained, and the value of the time constant ^τ can be ob ^¬ tained by calculation through ^ . Suppose that the time con ^¬ sumed by the closing of the circuit breaker is ^ , then the predicted residual voltage of the motor is

= TJ p ^T = 11 p ^T = 11 p ^T * p ^T = 11 p ^T

up ^cast ° ^u ° ^{e υ} ° ^{e 6 u e} _{f an} d the formula U _Mforecast = U 1 + 2* Δί + At) ¹

2 is obtained by expanding using Tayl formula .

In the residual mode which is already defined, the fre ^¬ quency attenuates linearly, therefore the following formula (3) can be used to predict the phase difference at the con ^¬ necting moment, ^forecas j_ _s obtained by calculation according

= ^(p + Αω _ΐ2 * At + i * a * At ²

to the following formula: ¹ , m which

A<p _ti -Αφ Am, -Am,

~ ^ι ι , _t h is the angular velocity differ- ence at the moment , ^ ^ω ' ^ι is the angular velocity difference at the moment , is the phase difference at the moment r is the phase difference at the moment , ^a is the attenuation rate of an angular velocity defined according to the residual transfer mode, j_ _s the time difference be- tween the moment and the moment , that is, the time pe ^¬ riod for the circuit breaker to close. By substituting the above formulae (2) and (3) into formula (1), the amplitude Qf £hg voltage vector difference can be obtained. According to another embodiment of the present invention, a fast bus transfer device comprises: a detection module, for detecting signals at the main power supply, the backup power supply and the bus; a calculation module, for receiving said signals, and calculating the amplitude U _forecast of the voltage vector difference between the bus and the backup power supply and calculating the phase angle difference <p _forecast between the bus and the backup power supply; a comparison module, for receiving AU _forecast and A(p _forecast , comparing A(p _forecast with its limit value AU _RTfTpammeter , and comparing with 90°; and a trans- fer module, for receiving the comparison results from the comparison module, and transferring the load on the bus to said backup power supply only when U _forecast is less than its limit value AU _{RTFTparameter} and tA(p _forecast is less than 90°. The signals detected by the detection module are various physical quantities that can be obtained without calculation in the present invention, and these physical quantities can be used as the basis for further calculation carried out us ^¬ ing various formulae in the present invention and are sent to the calculation module.

Said calculation module obtains by calculation according to the following formula:

Λ77 = ITT ¹ + TT ¹ - ? * TT * TT *ΓΓ>ςΛί7ΐ ττ

]_Q j_ _{n j} hlCh ^M /»' ^e ™» IS a f _. O ~ cast value of the motor's residual voltage, and ^Ua is the voltage of the backup power supply.

Said calculation module obtains ^ ^M f° ^recast by calculation ac- 15 cording to the following formula:

U _Mforecast = U _t (l + * At + ^ * { * At) ² ) _υ

^ ' , in which is the real-time am ^¬ plitude at the moment ; At j_ _s the time difference between the moment ^ ² and the moment , that is, the time period for

Λ=-Ι

the circuit breaker to close; and ^τ , ^τ being a time con-

20 stant.

Said calculation module obtains ^forecast calculation according to the following formula:

1 ₂

^forecast = ^A <P + ₂ * At + -*CC* At ^

¹ , in which ¹ is the phase dif-

25 ference at the moment ^ ² , ^ ^ω ' ² is the angular velocity dif ^¬ ference at the moment ^ ² , j_ _s the time difference between the moment ^ ² and the moment , that is, the time period for the circuit breaker to close, and ^a is the attenuation rate of an angular velocity defined according to the residual 30 voltage transfer mode.

Said calculation module obtains ^ by calculation accord-

ing to the following formula: ^{2 1} , in which is the real-time amplitude at the moment .

Said calculation module obtains and ^a by calculation according to the following formulae: and is the angular velocity difference at the moment , and is the phase difference at the moment . Fig. 4 illustratively shows the characteristic of an at ^¬ tenuated residual voltage in the present invention. As com ^¬ pared with the prior art shown in Fig. 1, the present invention has a real-time fast transfer section which is composed of two parts: a real-time fast transfer section 11 and a real-time fast transfer section 12, as well as an in-phase transfer section 2. The real-time fast transfer section in the present invention is not only greater than the fast transfer section 30 shown in Fig. 1, but also greater than the fast transfer section 3 shown in Fig. 4. The method and device according to the present invention can utilize the safe area for re-supply more fully, thereby achieving better technical effects.

Although embodiments of the present invention are illus- trated above, the described embodiments are not intended to exhibit all possible forms of the present invention. In addi ^¬ tion, the contents of the description are illustrative rather than restrictive. All kinds of variations and modifications can be made to the contents of the description by those skilled in the art without departing from the spirit of the present invention and the scope of the claims.