CN104635078B - Power cable indirect heat step experiment system and experiment method thereof - Google Patents

Abstract

The invention relates to a power cable indirect heat step experiment system and an experiment method thereof. The system comprises an arithmetic operation module, a power current adjusting module ACR (Automatic Current Regulator) and a PWM (Pulse Width Modulation) control loop module, wherein the PWM control loop module is used for providing corresponding control signals Upwmi to power electronic devices of a power amplifier and a current type inverter loop module connected with an output end of the PWM control loop module; the arithmetic operation module and the power current adjusting module ACR are connected in series with the PWM control loop module, the power amplifier and the current type inverter loop module in sequence and are connected with a power cable system and a load through a switch in sequence; the circuit between the power amplifier and the current type inverter loop module as well as the power cable is provided with a current sensing component; an output end of the current sensing component is connected with the arithmetic operation module through a current feedback loop module; the power cable system is connected with a conditioning circuit module through the temperature sensing component; the conditioning circuit module is connected with a personal computer; an output of the personal computer is diconnected with a cable system model temperature converter.

Description

A kind of power cable indirect thermal step experimental system and its experimental technique

Technical field

The present invention relates to the hot step experimental system and its experimental technique of a kind of power cable, more particularly to a kind of electric power electricity Cable indirect thermal step experimental system and its experimental technique.

Background technology

Since the eighties in 20th century, electricity has become people's production, an indispensable part of living, in order to meet people The demand of growing production, living standard to electricity, related researcher both domestic and external be devoted to always electric power it is safe, The efficient and reliable research for transmitting.Electric power is typically sent it to each electricity consumption user by cable from each power plant, distribution substation. Researcher is generally understood by the hot dynamic of power cable, studies its thermal model, system temperature, transmission power capability, longevity Life and reliability etc..

In electric power real-time transmission system in distributed power grid, and in real time using system information raising dynamic load pipe In the intelligent grid of reason ability, the heat dynamic analysis of power cable undoubtedly will play an increasingly important role.At present, hot step Experiment has become one of Basic Ways of heat dynamic analysis in people's research power cable.

Generally, people carry out in direct mode hot step experiment, i.e., using DTSE (directly hot step experiment) method.By step Definition understand that during DTSE is carried out, thermal power P of input cable should keep constant, the stable journey of P whether stable and P Degree directly determines success or not, the precision of experiment and the reliability of DTSE.

In the transmitting procedure of cable, thermal power P for flowing into cable is represented by the function of time t to electric power：

P (t)=W_d+nI_rms ²(t)R₀(1+α₂₀(θ(t)-20))(1+y_s+y_p)(1+γ_s+γ_a) (1)

In formula, W_dFor the dielectric loss of cable；N is the core number of cable；I_rmsFor the current effective value of cable transmission；θ T () is cable core nuclear temperature；R₀For 20 degrees Celsius when cable core D.C. resistance；α₂₀For cable core nuclear temperature coefficient；y_sFor The skin effect coefficient of cable；y_pThe kindred effect coefficient of cable；γ_sFor the sheath fissipation factor of cable；γ_aFor the first of cable Fissipation factor.

For given cable system, W_dIt is related with the voltage of power grade (such as 36kV, 110kV etc.) of cable transmission, certain The impact that the small range of voltage fluctuates to it in one grade is little.Each coefficient, factor substantially constant in formula (1), cable core Temperature θ (t) can over time be elapsed and is continually changing, until cable system enters thermal equilibrium state, thermal equilibrium state is referred to The temperature of one system does not change with the time, in thermal equilibrium state when, flow into system thermal power be equal to outflow system Thermal power.

From formula (1), P and I_rms, there is non-linear relation between θ (t), to allow P constant, I_rmsShould be with θ's (t) Change and nonlinear change occurs.When P is constant, θ (t) and time allow P constant I into multi-order index relation_rmsIts change It is very complicated nonlinear change, and then allows P constant I_rmsControl system is also extremely complex.

According to formula (1), existing DTSE it is critical only that and allow thermal power P of input electric power cable to keep constant, and it is right to pass through I_rmsThe control direct control constant to realize P.

As shown in figure 1, thermal power instruction U_gPRepresent the thermal power desired value for flowing into power cable, U_fPRepresent and flow into electric power The thermal power actual value of cable；U_giRepresent the current expected value for flowing into power cable, U_fiRepresent the electric current reality for flowing into power cable Actual value.APR is thermal power adjustment unit, and its control law can be according to circumstances proportional integral, PID etc..Convolution (1), APR outputs U_giTo flow into the current expected value of power cable, with the thermal power of constant inflow power cable.ACR is electric power Current regulation unit, its control law can adoption rate integration, PID, adaptive control laws etc..Allow and flow into cable Power current approaches as early as possible or reaches its desired value U_giIt is the basic task of the unit.PWM control loops are the electricity of inversion circuit Power electronic device provides corresponding control signal U_pwmi.Inversion circuit is converted into utility power and U_pwmiCorresponding current power stream Enter power cable.Because in laboratory environment, the voltage of power typically fluctuation of a certain voltage level (in units of kV) is less, To W_dVery little is affected, W can be approximately considered_dIt is constant.

As shown in figure 1, DTSE is two ring feedback control loops, outer shroud realizes the constant control of thermal power, inner ring controlling stream Enter the power current of cable, allow it to approach desired value U of power current_gi.Because cable temperature is elapsed over time constantly in many Rank exponential relationship changes, and is known by formula (1), and power current is accomplished by being constantly tracked this change of temperature.Start in hot step Stage, cable temperature changes quickly, and inner ring control unit needs very strong quick-reaction capability, could control electric current preferably with The change of upper temperature.Electric current does not once catch up with this change, and thermal power is just constant not to know clearly, so as to cause hot step experiment not smart Really, it is unreliable.It follows that DTSE has complex structure, the quick performance of inner ring power current control, trace performance are required very The shortcomings of high and high cost.

In fact, the multi-order index relation according to formula (1) and between θ (t) and time t, always can obtain maintaining P constant Power current I_rmsWith regard to function f (t) of time t, i.e. I_rmi=f (t).If I_rmsRule according to f (t) changes, and P will be protected Hold constant.Control program based on this thinking is as shown in Fig. 2 U_gPRepresent the thermal power desired value for flowing into power cable；U_giGeneration Surface low enters the current expected value of power cable, U_fiRepresent the current actual value for flowing into power cable.According to formula (1) and with reference to θ (t) With the multi-order index relation between time t, f (t) generators produce can the power current desired control of stable cable thermal power believe Number U_gi.ACR is power current adjustment unit, and its control law can adoption rate integration, PID, adaptive control laws Deng.The power current for flowing into cable is allowed to approach or reach its desired value U as early as possible_giIt is the basic task of the unit.

PWM control loops provide corresponding control signal U for the power electronic devices of inversion circuit_pwmi.Inversion circuit is by public affairs It is converted into electric power and U_pwmiCorresponding power current flows into power cable.

As shown in Fig. 2 it is to instruct f (t) generator and right by current waveform that the constant of cable thermal power is flowed in scheme The instruction accurately and fast follows indirect realization.The constant precision of cable thermal power depends primarily on current waveform instruction f Trace performance of the acquisition precision and inversion circuit of (t) to instruction f (t).Known by formula (1), accurately to determine f (t), need cable The accurate physical parameter of system and its thermal model characteristic parameter.For concrete cable system, these parameter high costs are accurately obtained. Cable temperature is in over time multi-order index relationship change, is known by formula (1), and current waveform instruction f (t) changes over more multiple It is miscellaneous.In the hot step incipient stage, fast-changing cable temperature determines the quick change of f (t), and this needs current control link And inverter etc. could control this change that power current preferably keeps up with f (t) with very strong dynamic response capability.Thus Understand, the shortcoming of this technical scheme is：Precision is not high, and this is determined by the indirect control of thermal power, in addition, f (t) is general not Can be very accurate；The quick performance of power current controlling unit, inverter etc., trace performance require very high；High cost.

The content of the invention

For above-mentioned technical problem, between the high power cable of a kind of simple system of present invention offer, low cost and reliability Connect hot step experimental system and its experimental technique.

To solve above-mentioned technical problem, the technical solution used in the present invention is：A kind of power cable indirect thermal step reality Check system, it is characterised in that：It includes one for the current expected value U to flowing into power cable_giWith current actual value U_fiCarry out The arithmetical operation module of arithmetical operation, one is used to make the power current of inflow power cable approach or reach desired value U_giElectric power Current regulating module ACR, one be used for be the power amplifier and current mode inversion circuit module being connected with its output end power electronics device Part provides corresponding control signal U_pwmiPWM control loop modules；The arithmetical operation module, the power current adjust mould Block ACR successively with the PWM control loops module, the power amplifier and current mode inversion circuit block coupled in series and by one switch according to One power cable system of secondary connection and a load；The power amplifier and current mode inversion circuit module and the power cable system it Between circuit on a current sensing components and parts are set, the output end of the current sensing components and parts passes through a current feedback loop mould Block is connected with the arithmetical operation module；The power cable system is by a temperature sensing components and parts and a conditioning circuit module Connection, the conditioning circuit module connects a personal computer, the personal computer and cable system model temperature converter Two-way communication.

N rank thermal model of the cable system model temperature converter based on the power cable system, the n ranks hot-die Type includes the RC network of n ranks series connection, and the RC network of n ranks series connection is related to flow into thermal power p of the power cable system (t), temperature θ of power cable system outside air_a, the i-th rank RC network temperature θ_i, the i-th rank RC network thermal resistance R_i, the i-th rank RC network thermal capacitance C_i, flow into the i-th rank RC network thermal capacitance in thermal power p_i,1, flow through the i-th rank RC network thermal resistance simultaneously Flow into thermal resistance p in lower single order RC network_i,2, wherein 1≤i≤n.

The cable system model temperature converter follows following Heat transfer law：

In formula, θ_iT () is the temperature of cable the i-th rank RC network；θ_i+1T () is the temperature of cable i+1 rank RC network.

A kind of experimental technique of power cable indirect thermal step experimental system, comprises the following steps：

1) heating period, temperature sensing components and parts gather the temperature signal of power cable system, and by modulate circuit mould Block is stored in temperature signal on the hard disk of personal computer, the display real-time monitoring power cable system of personal computer Warm status, when monitoring that power cable system reaches thermal equilibrium state S₀When, closing a switch, current sensing components and parts are perceived Reach thermal equilibrium state S_pPower current actual value U_fiJing current feedback loops module transfer is to arithmetical operation module, arithmetic fortune Module is calculated by U_fiWith the current expected value U for flowing into power cable_giArithmetical operation is carried out, arithmetic operation results pass through the electric power After the regulation of current regulating module ACR, PWM control loop modules, power amplifier and current mode inversion circuit module collective effect are allowed, profit Constant current electric power is produced with utility power, constant current flows into power cable system, into the heating period；From power cable system In the thermal power that discharges rise to p and no longer change, power cable system enters thermal equilibrium state S_p, the heating period terminates；

2) the heat energy stage is freely discharged, power cable system enters S_pAfter state, switch is disconnected, power cable system will be deposited Heat energy in Chu Qi freely discharges；Power cable system is released after heat energy therein, and its temperature will no longer change, it Initial S is returned again₀State, temperature response curve θ of the power cable system in this stage is gathered by personal computer_CABL(t)；

3) analysis temperature stage, temperature response curve θ that personal computer is gathered_CABLT () sends into cable by serial ports System model temperature divertor, cable system model temperature converter utilizes θ_CABLT () analyzes cable system thermal power for p's Hot step temperature response curve θ (t), then, θ (t) is sent back to personal computers by serial ports, and experiment terminates.

Due to using above technical scheme, its technique effect for reaching is the present invention：1st, present invention obviates and be directly realized by The thermal power for flowing into cable is allowed to be always maintained at constant this basic demand in hot step experiment, with a kind of inexpensive, succinct, reliable Mode obtain the temperature response curve that the experiment of hot step needs to obtain indirectly, significantly reduce the dynamic tracking of experimental facilities Performance requirement, so as to significantly reduce the cost that hot step is tested, the precision, the reliability that improve experiment.With good Social benefit, economic benefit.2nd, because the present invention is using constant current controlling device and current inversion loop, to ensure cable system energy Enough enter and keep thermal equilibrium state S corresponding with thermal power p_p, into S_pHow the thermal power of cable has no to experiment before state Affect, therefore the present invention is not high to the performance requirement of constant current controlling device and current inversion loop, the constant current control of general performance Device processed and current inversion loop meet requirement.Because temperature is process variable, general temperature acquisition system and PC systems can Meet requirement of real-time.

Description of the drawings

Below in conjunction with the accompanying drawings the invention will be further described：

Fig. 1 is the direct constant control scheme schematic diagram of power cable thermal power；

Fig. 2 is the constant scheme schematic diagram of power cable thermal power of Current Waveform Control；

Fig. 3 is the n rank thermal model schematic diagrames of power cable system of the present invention；

Fig. 4 is the overall structure diagram of the experimental system of the present invention；

Fig. 5 is cable copper core and casing ambient air temperature curve synoptic diagram in embodiment；

Fig. 6 is the hot step copper core temperature response curve schematic diagram of cable in embodiment.

Specific embodiment

For the ease of understanding the present invention, the following detailed description of the experimental principle of the present invention：

As shown in figure 3, setting up the n rank thermal models of power cable system, it includes the RC network that n ranks are connected, wherein, W is Thermal source；P (t) is the thermal power for flowing into cable system, is calculated by formula (1)；θ_aFor cable system outside air Temperature；θ_iFor the temperature of the i-th rank RC network；R_iFor the thermal resistance of the i-th rank RC network；C_iFor the thermal capacitance of the i-th rank RC network；p_i,1For stream Enter the thermal power in the i-th rank RC network thermal capacitance；p_i,2To flow through the i-th rank RC network thermal resistance and flowing into the thermal resistance in next network.

θ_i、R_i、C_i、p_i,1、p_i,2Follow the Heat transfer law of formula (2)：

In formula, θ_iT () is the temperature of cable the i-th rank network；θ_i+1T () is the temperature of cable i+1 rank network.

First, constant thermal power p (t) flowed in power cable system, power cable system is from a certain thermal balance shape State S₀Start, the Warm status of cable system change according to the thermal model shown in Fig. 3 and with the rule of formula (2), it is concrete to become Turn to：Each rank RC network temperature gradually rises in thermal model, and increasing thermal energy storage is in thermal capacitance C_iIn, pushing away over time Move, temperature raises more and more slower, and heat absorption obtains more and more slower, and heat energy discharges more and more faster to outside thermal model.Work as heat The each rank RC network temperature of model is no longer raised, heat energy not re-absorption when, the output thermal power of thermal model is equal to input thermal power p T (), thermal model enters thermal equilibrium state S corresponding with p (t)_P, now, directly hot step experiment just finishes, and this process is The heating period of thermal model.Record thermal model has just obtained the hot rank of power cable system from experiment is started to temperature now Jump experimental temperature response curve, is designated as θ (t).

Thermal source W is closed, now thermal model is flowed into without thermal power p (t), the Warm status of power cable system are just from thermal balance shape State S_PBeginning changes according to the thermal model shown in Fig. 3 and with formula (2) rule, is stored in thermal capacitance C_iHeat energy through thermal resistance R_iDischarge to outside thermal model, temperature starts to reduce, and heat energy is fewer and feweri, and heat energy outwards discharges more and more slower, and temperature also drops It is increasingly slower, heat energy therein is finally released, its temperature no longer changes, and comes back to thermal equilibrium state S₀, the process is electric The heat energy release stage of cable system.Cable is recorded from thermal equilibrium state S_PTo S₀Temperature response curve, be designated as θ_CABL(t).For just In analysis, thermal model during the entire process of above-mentioned heating, heat energy release by means of air-conditioning or fan facility by thermal model around The θ of temperature_aKeep constant.

Due to above-mentioned S₀To S_PAnd S_PTo S₀It is two processes being closely related, the two processes are in the heat shown in Fig. 3 The rule shown in formula (2) is completed and followed in model, therefore, θ (t) and θ_CABLClose contact is there is between (t).

Assume θ_nT ()=θ (t), by formula (2) p can be calculated_n,1(t)、p_n,2(t), from the figure 3, it may be seen that p_n-1,2(t)=p_n,1 (t)+p_n,2T (), by formula (2) θ can be further calculated_n-1T (), on this basis, can analyze p_n-1,1(t).Similarly, P can successively be calculated_n-2,2(t)、p_n-2,1(t), p_n-3,2(t)、p_n-3,1(t) ... ..., p_1,2(t)、p_1,1(t).When initial, cable system System is in Warm status S₀, the temperature of each rank RC network is ambient temperature θ_a.The heating period start in a flash, due to θ₁=θ₂=θ_a, then p_1,2=0, p_1,1=p.

I.e. now all of thermal power is stored entirely in thermal capacitance C₁In, to be known by formula (2), these thermal powers can allow θ₁Raise. With θ₁Rising, p_1,2Become larger by 0, p_1,1Tapered into by p.When thermal model enters Warm status S_PAfterwards, p_1,2P is risen to by 0, p_1,1It is down to 0.In the heating period, the thermal power of each rank RC network is just, will thermal energy storage in thermal capacitance C_iIn.Release in heat energy Decontrol and begin in a flash, to flow into power cable without electric power, then p_t=0, flow through R₁Thermal power p_1,2=p (such as formula (2), this Size thus when θ₁With θ₂Between difference determine) can only be by C₁There is provided, therefore C₁The thermal power for now discharging is p.Known by formula (2), heat The release of power allows temperature θ₁Reduce, p_1,2Taper into from p, C₁The thermal power of release is also tapered into.It follows that in heating With heat releasable corresponding period, flow through thermal capacitance C₁Thermal power size be the same, different is in opposite direction：The former deposits Heat accumulation power, the latter's release thermal power.For other each rank thermal capacitances in Fig. 3, identical conclusion can be similarly analyzed.Cause This, if known θ (t), can calculate as described above p_n-1,1T (), takes p_n-1,1T the opposite number of () simultaneously then can be analyzed according to formula (2) θ_CABL(t).In the same manner, if known θ_CABLT (), can calculate p_n-1,1T (), takes p_n-1,1T the opposite number of () simultaneously then can divide according to formula (2) Separate out θ (t).

Obviously, S_PTo S₀S is compared in the realization of physical process₀To S_PThe realization of physical process is easy, because, S_PTo S₀Physical process Constant thermal power is not needed.Therefore, the present invention utilizes θ based on above-mentioned principle_CABLT () analyzes θ (t), i.e., obtain heat first The cable temperature curve θ in stage can be discharged_CABL(t), with each rank thermal capacitance C of cable_iOn thermal power go out hot step temperature for medium analysis Degree response curve θ (t).

As shown in figure 4, being based on above-mentioned principle, power cable indirect thermal step experimental system is set up, it includes that an arithmetic is transported 1 is calculated, for flowing into the current expected value U of power cable_giWith current actual value U_fiArithmetical operation；One connection arithmetical operation 1 Power current adjustment module ACR2, the power current for making inflow power cable approaches as early as possible or reaches desired value U_gi；One connects The PWM control loops 3 of ACR2 are connect, for for the power electronics device of the power amplifier being connected with its output end and current mode inversion circuit 4 Part provides corresponding control signal U_pwmi；The output end of power amplifier and current mode inversion circuit 4 by switch 5 be linked in sequence electric power electricity Cable system 6 and load 7；Pass through a current sensor 8 on circuit between power amplifier and current mode inversion circuit 4 and power cable 5 The current actual value U of power cable will be flowed into_fiTransmitted to arithmetical operation 1 by a current feedback loop 9.Power cable system 6 One modulate circuit 11 is connected by a temperature sensor 10, modulate circuit 11 is connected with a personal computer (PC) 12, individual's meter Calculation machine 12 is bi-directionally connected with cable system model temperature converter 13.

Based on the experimental technique of power cable indirect thermal step experimental system, comprise the following steps：

1) heating period, temperature sensor 10 gathers the temperature signal of power cable system 6, and will by modulate circuit 11 Temperature signal is stored on the hard disk of personal computer 12, the display real-time monitoring power cable system 6 of personal computer 12 Warm status, when monitoring that power cable system 6 reaches thermal equilibrium state S₀When, 5, the Jing current sensors 8 that close a switch are perceived To power current value actual value U_fiJing current feedback loops 9 are transmitted to arithmetical operation 1, and arithmetical operation 1 is by U_fiIt is electric with electric power is flowed into The current expected value U of cable_giArithmetical operation is carried out, arithmetic operation results allow PWM control loops 3, power amplifier after the regulation of ACR2 And the collective effect of current mode inversion circuit 4, constant current electric power is produced using utility power, constant current flows into power cable system 6, into the heating period.The temperature of power cable system 6 begins to ramp up, and due to current constant, is known by formula (1), flows into power cable The thermal power of system 6 is continuously increased with the rising of temperature.When the temperature of power cable system 6 no longer changes, electric power is flowed into The thermal power of cable system 6 rises to p and is not further added by, and the thermal power discharged from power cable system 6 rises to p and no longer becomes Change, power cable system 6 enters thermal equilibrium state S_p, the heating period terminates.

2) the heat energy stage is freely discharged, power cable system 6 enters S_pAfter state, switch 5, power cable system 6 are disconnected The heat energy that will be stored in it freely discharges, and heat energy discharges more and more slower, and temperature also reduces more and more slower.Power cable system System 6 is released after heat energy therein, and its temperature will no longer change, and it returns initial S again₀State, by personal computer Temperature response curve θ of 12 power cable systems 6 for gathering this stage_CABL(t)。

3) analysis temperature stage, temperature response curve θ that personal computer 12 is gathered_CABLT () sends into electricity by serial ports Cable system model temperature divertor 13, heat of the cable system model temperature converter 13 based on the power cable system shown in Fig. 3 Heat transfer law shown in model and formula (2), the thermal power with each RC network of thermal model in thermal capacitance as intermediary, using θ_CABL T () analyzes hot step temperature response curve θ (t), then, θ (t) is sent back to personal computers 12 by serial ports, and experiment terminates.

Embodiment：So that, equipped with the concrete of building house wall, the central authorities of concrete place one in the wooden box body of 3m length The pvc pipe of individual a diameter of 35mm, the central authorities of pvc pipe have disposed the 0.6/1.0kV domestic type copper core cables of the 6942XL types of 3m length As a example by.The maximum temperature that the cable copper core is allowed when room temperature is 30 DEG C is 90 DEG C.Constant current controlling is employed in the present embodiment, electricity Resistive load and Pico temperature acquisition systems, the sampling period is 1 second.Cable system is 3 levels system, the feature of first-order system Parameter is R₁=0.392859, C₁=87.089645；The characteristic parameter of second-order system is R₂=1.743539, C₂= 286.393508；The characteristic parameter of third-order system is R₃=0.839505, C₃=3115.072372, thermal resistance, the unit of thermal capacitance Respectively DEG C .m/W, J/ DEG C .m.The power current of controller output is 19A in the present embodiment, and voltage is 230V, and frequency is 50Hz.Temperature sensor gathers the copper core temperature and casing ambient air temperature of power cable system in whole experiment process (such as Shown in Fig. 5), it can be seen that the copper core temperature of power cable has almost no change when rising to 26.97 DEG C, this phase Between power current maintain essentially in 19A, thermal power now can be calculated as p=2.2623W/m according to formula (2).This state Maintain more than ten minutes, it is believed that cable system enters thermal equilibrium state S_p, now testing has been carried out 17084 seconds, heats rank Section terminates.

Close electric supply, experiment freedom of entry release heat energy stage.That is the 17084th second and temperature afterwards are in Fig. 5 θ_CABL(t).By θ_CABLT () is sent into after power cable system model temperature converter, obtain the hot step copper core of power cable system Temperature response curve θ (t) (as shown in Figure 6).In figure, the temperature that solid line type is represented is by changing the copper core temperature for getting, void Line is the cable model input 2.2623W/m hot merits in the PLECS environment (environment is mainly used in hot emulation experiment) of Matlab The hot step temperature-responsive simulation curve of cable copper core during rate.As seen from the figure, the two curves are obtained very well, indicate the party The hot step temperature response curve that method is obtained is very accurate, reliable.

It can be that professional and technical personnel in the field realize or use that above-mentioned embodiment is intended to illustrate the present invention, to above-mentioned Embodiment is modified and will be apparent for those skilled in the art, therefore the present invention is included but is not limited to Above-mentioned embodiment, it is any to meet the claims or specification description, meet with principles disclosed herein and novelty, The method of inventive features, technique, product, each fall within protection scope of the present invention.

Claims (4)

1. a kind of power cable indirect thermal step experimental system, it is characterised in that：It includes one for flowing into power cable Current expected value U_giWith current actual value U_fiThe arithmetical operation module of arithmetical operation is carried out, one is used to make inflow power cable Power current approaches or reaches desired value U_giPower current adjustment module ACR, one be used for be the power amplifier being connected with its output end And the power electronic devices of current mode inversion circuit module provides corresponding control signal U_pwmiPWM control loop modules；Institute State arithmetical operation module, power current adjustment module ACR successively with the PWM control loops module, the power amplifier and electricity Flow pattern inversion circuit block coupled in series is simultaneously sequentially connected a power cable system and a load by a switch；The power amplifier and electric current One current sensing components and parts, the current sensing are set on the circuit between type inversion circuit module and the power cable system The output end of components and parts is connected by a current feedback loop module with the arithmetical operation module；The power cable system leads to Cross a temperature sensing components and parts to be connected with a conditioning circuit module, the conditioning circuit module connects a personal computer, described Personal computer and cable system model temperature converter two-way communication.

2. power cable indirect thermal step experimental system as claimed in claim 1, it is characterised in that：The cable system model N rank thermal model of the temperature divertor based on the power cable system, the n ranks thermal model includes the RC network of n ranks series connection, n The RC network of rank series connection is related to flow into thermal power p (t) of the power cable system, the power cable system outside Temperature θ of air_a, the i-th rank RC network temperature θ_i, the i-th rank RC network thermal resistance R_i, the i-th rank RC network thermal capacitance C_i, flow into Thermal power p in i-th rank RC network thermal capacitance_i,1, flow through the i-th rank RC network thermal resistance and flow into the thermal resistance in next rank RC network p_i,2, wherein 1≤i≤n.

3. power cable indirect thermal step experimental system as claimed in claim 2, it is characterised in that：The cable system model Temperature divertor follows following Heat transfer law：

$p_{i,1}=C_i\frac{{\mathrm{d\θ}}_i\left(t\right)}{dt}$

$p_{i,2}=\frac{{\mathrm{\θ}}_i\left(t\right)-{\mathrm{\θ}}_{i+1}\left(t\right)}{R_i}$

In formula, θ_iT () is the temperature of cable the i-th rank RC network；θ_i+1T () is the temperature of cable i+1 rank RC network.

4. a kind of experimental technique of the power cable indirect thermal step experimental system as described in any one of Claim 1-3, including Following steps：

1) heating period, temperature sensing components and parts gather the temperature signal of power cable system, and will by conditioning circuit module Temperature signal is stored on the hard disk of personal computer, the hot shape of the display real-time monitoring power cable system of personal computer State, when monitoring that power cable system reaches thermal equilibrium state S₀When, close a switch, what current sensing components and parts were perceived reaches Thermal equilibrium state S_pPower current actual value U_fiJing current feedback loops module transfer is to arithmetical operation module, arithmetical operation mould Block is by U_fiWith the current expected value U for flowing into power cable_giArithmetical operation is carried out, arithmetic operation results pass through the power current After the regulation of adjustment module ACR, PWM control loop modules, power amplifier and current mode inversion circuit module collective effect are allowed, using public affairs Constant current electric power is produced with electric power, constant current flows into power cable system, into the heating period；Release from power cable system The thermal power of releasing rises to p and no longer changes, and power cable system enters thermal equilibrium state S_p, the heating period terminates；

2) the heat energy stage is freely discharged, power cable system enters S_pAfter state, switch is disconnected, power cable system will be stored in Heat energy in it freely discharges；Power cable system is released after heat energy therein, and its temperature will no longer change, and it is returned again Initial S₀State, temperature response curve θ of the power cable system in this stage is gathered by personal computer_CABL(t)；

3) analysis temperature stage, temperature response curve θ that personal computer is gathered_CABLT () sends into cable system mould by serial ports Type temperature divertor, cable system model temperature converter utilizes θ_CABLT () analyzes the hot step that cable system thermal power is p Temperature response curve θ (t), then, θ (t) is sent back to personal computers by serial ports, and experiment terminates.