DESIG AND ANALYSIS OF Z-SOURCE INDUCTOR TYPE CIRCUIT BREAKER FOR MICRO GRID APPLICATIONS

DESIG AND ANALYSIS OF Z-SOURCE INDUCTOR TYPE CIRCUIT BREAKER FOR MICRO GRID APPLICATIONS

ABSTRACT

This paper present implementing an inductor based circuit breaker for micro grid with renewable energy source being visualized as dc power systems. The main purpose of micro grid dc power system to eliminate the power conversion steps i.e. step down and step up voltages. According to the system components there are various loads such as solar panel, fuel cells and batteries. Power conversion which is readily available. The main limitation is that interrupting a current arc and arc current doesn’t zero. This paper present new type of circuit breaker implementing provide an efficient power conversion between source and load in wide range of electric power conversion applications. Here Circuit breaker important role to protect the system from under abnormal condition. It works based on inverter principle, and also utilized for a short conduction path which lies between breaker and load as well as mutual coupling to automatically and rapidly switch off response to a fault. In this system proposed crowbar type switch in the output so that it can act as a dc switch. Mathematical and simulation analysis the proposed topology of the new switches are included.

Keywords: Circuit Breaker, Mutually Coupled Inductor, Power Transmission, Thyrister Circuit, Fault Location, DC-DC  Inverter.

1. INTRODUCTION

Present  days most of the  power transmission and distribution on alternating current(AC) power, but some specific applications instead of AC current where as DC current (dc) power is more efficient to use such electric ships, data counters, home applications, microgrid with renewable energy. DC power is often used in industries and applications that require a long duration discharge over a long time period. In fact, high voltage dc voltage more efficient than the high voltage ac voltage. As researchers for the protection of dc power systems, fault protection circuit breaker are used. Its protect the system from the fault condition circuit breaker is a switch it’s protect the system from the fault its automatically operates at fault condition to protect the electric circuit, Hence it is known as a protective device. The main function is fault is detected it interrupt the current. Unlike the fuse and circuit breakers can be reset manually or automatically and it can be replaced. there are different range of circuits breakers are available depends on applications we are use different range from small to large applications.Comapre to DC circuit breakers AC circuit breaker having so many faults. In dc present only short circuit are open circuit fault but both the faults cause damage to either source or load. For the protection of the system we are introducing a new type of circuit breaker with Z-source. Z-Source inductor act as a buck-boost converter it can reduce the fault which is decrease or increase the magnitude of power during the fault condition that means its act as a short circuit, that means voltage becomes zero and output current increases this excess to  increase of current may damage source or load. The most dis advantage of other circuit breakers like mechanical and solid breakers the excess amount of output current is wasted. In order to overcome this problem develops Z-source this current will stored inductor during the fault condition after clearing the fault the stored current will be added to the source current and transfer to the load that means Z-source function is act as similar to a Buck-Boost converter.

1. fault sensing using a path from the source

1. Fault sensing using a path from the breaker

Fig (1) . Fault sensing techniques

Figure (1a) shows a typical arrangement of a circuit breaker inserted between source and load. In this circuit source current is controlled for fault detection current.

Fig (1b) shows a capacitor can be connected to ground within the circuit breaker. This method is very efficient for detecting transient current and is used in electrical drives for detection of shoot-through small capacitor in series with some type of current sensor can be connected to the dc drive. Shoot through fault create an impulse of a current in this capacitor and the detection can immediately switch off the drive signals. Otherwise short path could be added to dc circuit breaker for fast detection fault. Instead of control the main current between source and load and allowing the source to experience the fault current for a while, the short path between the added capacity and load readily indicate the fault.

Fig (2) circuit breaker with Z-source creating a short through path

Fig (2) which shows a Z-source dc circuit breaker connected between load and source. Hence source current can be observed for detection of fault. We are connecting capacitor in series with a sensor and it parallel to the circuit breaker its useful to detect the transient currents and sensor sense the fault, gives signals to the circuit breaker. Therefore here creates the short through path for faults and capacitor impulse current created and detected fault and switch off the signal. Z-source response very fast during the fault time.

1. PROPOSED DC CIRCUIT BRAKER:

In this paper discussing about a dc circuit breaker which is for protecting purpose during the fault condition. The block diagram of dc circuit breaker consists of dc source, switch, load and sensor connected between switch to load and sense the signal during the fault condition.

Figure3. The Proposed Dc Circuit

Above diagram shows proposed dc circuit. Under normal steady state condition current flows source to load through the SCR and coupled inductor. Under abnormal condition fault occurs on load side will cause an impulse current i_c in the short path consist of capacitor and secondary winding consist of coupled inductor with turns ratio, this current is reflected to the primary and forced the scr current is zero; in this time the SCR is turn off and turns ratio N₁/N₂ and also breaker does not identify a large change in load as a fault.

Fig4. A Variation of The Proposed Dc Circuit Breaker

An alternate approach to the proposed breaker shown in fig 4.in this proposal, the main path current flows through the primary and secondary windings.

1. DESIGN AND ANALYSIS
2. Step load analysis:

One of the main advantages of the proposed dc switch is its ability to remain on during a step change in load. Therefore, it is useful to know how to design the transformer component and what type of load will cause the breaker to switch off. From fig1 neglecting transformer magnetizing current

I_S=I₀= – (N₂/N1)I_C…………………………………………………………..(1)

For the steady state operation, the capacitor current zero and the source current is equal to the output current. Assuming that a sudden changing in output current is entirely represented by a change in capacitor current, that is,

∆i_c≈∆i_o……………………………………………………………………..(2)

By transformation action,

∆i_s≈-N₂/N₁∆I_C≈-N₂/N₁∆I_{0 ………………………..………………………….(3)}

_{NOW, with an initial output current of}

I_S=I_{0………………………………………………………………….. (4)}

The response of the source current change in output current will be

I_s=i₀ –N₂/N₁∆I₀…………………….…………………………….(5)

This source current and SCR current become a zero when the change in output meets the condition

∆i₀ › (N₁/N₂)I₀………………………………………….(6)

Therefore, (6) can be used to determine the amount of change in output current result it gives the breaker switching off. It is useful to select a turn’s ratio of the transformer to ensure that breaker will not switch off during expected load transient.

1. CIRCUIT DESIGN:

For the design of circuit consider following circuit parameters

The breaker designs starts with choosing a wire, and carrying out a design for the transformer primary winding. the cross sectional area of wire 0.82mm².the transformer is going to an air-cored type and square capacitor dimensions of 70mm by 57.5mm.assumed leakage inductance is 5%.the value of resistance is low value.

1. CIRCUIT ANALYSIS

Fig (5). Equivalent Circuit of the Proposed Dc Breaker.

Show the equivalent circuit of the proposed breaker with SCR. In this circuit, neglect the leakage reactance and Resistance. The series combination of R and C and Z_L is the parallel combination of R_l and C_l is gives the equivalent circuit Z_RC. L_m1 and L_m2 are magnetizing inductance of primary and secondary of transformer respectively.

Voltage transformation function is

…………(7)

Impedance from source

…………(8)

Where

L₁₂=√L_m1L_m2

1. SIMULATION DETAILS:

Fig (6) Simulation Circuit For Change In Load

Above circuit reprents the simulink circuit for change in load. Under the normal condition the current flows from source to the load. In this simulink circuit consist of thyristor which acts as a circuit breaker and its mutually coupled inductor is the current flows through the primary side will be the same on secondary side there will be change the current one coil to other coil they are magnetically coupled. Under abnormal condition that means when the fault occurs circuit breaker sense the signal and z-source inductor replaced.

Fig (7).Sub Circuit of Load Variation

PARAMETERS FOR THE TEST

The source voltage 120V given for the pure resistive load. the source and output current when there is a change in load  from 60ohms to 18.5ohms the output current will be 3A after 0.8msec.this is under the normal condition. Under abnormal condition the current change from 3A to 6A.in this case capacitor current flows back to the source. Therefore circuit breakers switch off. The SCR is in closed position and the source current reaches to 6.2A and settle down at 6A.

Fig (8). Source Current and Load Response During Change In Load

1. UNDER FAULT CONDITION FOR IDEAL DC CIRCUIT:

Principle and operation of a circuit breaker under normal condition contacts of circuit breaker closed under abnormal condition means when the fault exist on the line contacts of circuit breaker open here we are establishing a fault as short circuit by connection a switch parallel to the load.

Fig (9).Simulink Circuit During The Fault Condition

In above circuit source voltage is 120V and the load resistance is 18.5ohms.at this load resistance act as a short circuit. The charactestices of currents and voltage across each parameter shown below in simulink

.

Fig(10) Simulink Response During The Fault Condition

Initially that means under normal condition circuit breaker closed time up to 0.2msec.after the 0.2msec circuit breaker contacts open during this condition voltage across the load is zero means act as short circuit load current is increase its effect on transformer and capacitor goes to discharge in this condition after sometimes SCR across the voltage will be positive it goes to negative and its magnitude is equal to the source voltage, then the diode switches ON for stopping the response. After the 0.2msec voltage across the load is zero then SCR is open load current is 50A and capacitor starts discharge and SCR goes to negative value.

1. PRACTICAL CONSIDERATION

In practical consideration prototype of the proposed circuit breaker constructed according to following consideration parameters

In this case we are checking that how dc circuit breaker may operate practically for power system and medium voltage design will be carried out for this type of breakers. Here we consider the leakage reactance of the transformer, source impedance and rate of fault.

The proposed dc circuit breaker inserted into a medium-voltage dc system. two modifications are consider in this system. first modification is RC impedance in the previous design has been replace with pure capacitor. In addition charging resistor placed in series. the purpose of resister initially charge the capacitor. That is voltage established across the SCR. The modification SCR shown in below

Fig (11).Power System With Modification Dc Switch

The medium voltage dc system has source voltage is 1000V and power level of 100KW.the source inductance of 10µH.Let’s assume leakage reactance 10% and consider the turns ratio. Transformer is air cored with solenoid structure.

Above table represents the parameters for dc power system circuit. Simulation results of the proposed breaker demonstrating closing and opening ability. from fig(11) first,S₁ is fired and the capacitor is charge through the R_C.since the time constant here is 10ms,the capacitor fully charge at 55ms.at this point, the breaker supporting a 100KW load. at 65ms capacitor discharge in the transformer secondary and causing the proposed circuit to switch off. This added SCR can be used to switch off the load.

Fig (12). Simulation Demonstrating Switch-Off Capability

Fig (13). Simulation Demonstrating Fault Handling

Above fig (13) shows simulink response for fault condition. at starting the breaker 30KW load when load suddenly increased to 100KW.for this change of load breaker does not switch off. And also increase voltage across the transformer 250V spikes this voltage very useful to differentiate between a change in load and fault. During the fault condition voltage across the transformer goes to 460V.haence this voltage V_T is useful to identify the fault. And control signal measure the voltage of V_T may remove the spikes.

CONCLUSION

As a dc source and micro grids become a more prevalent, solution sought for dc switches and circuit breakers. The main purpose of micro grid dc power system to eliminate the power conversion steps i.e. step down and step up voltages. Recently we are using different circuit breakers such as ac circuit breakers, solid-state circuit breakers. In this paper used solid-state circuit breaker with z-source inductor its automatically operated and eliminate the spikes during the fault. Amplitude of voltage increase or decreased here z-source function act as a buck-boost converter. For the designing of a transformer we are used turns ratio to determine amount of transient current that will be identified as a fault. Analysis and design demonstrate the proposed breaker response to step change in load and a fault here breaker doesn’t produce the ringing resonance in the source current.

REFERENCES

[1] R. Cuzner, D. MacFarlin, D. Clinger, M. Rumney, and G. Castles, “Circuit breaker protection considerations in power converter fed dc systems,” in Proc. IEEE Electr. Ship Technol. Symp., Apr. 2009, pp. 360–367.

[2] B. Bolanowski and F.Wojcik, “A fast dc hybrid circuit breaker,” presented at the IEEE Colloq. Electronic-Aided Current-Limiting Circuit Breaker Developments Applications, London, U.K., Nov. 1989.

[3] A. Pokryvailo and I. Ziv, “A hybrid repetitive opening switch for inductive storage systems and protection of dc circuits,” in Proc. IEEE Power Modulator Symp. High-Voltage Workshop, 2002, pp. 612–615.

[4] C.Meyer,M. Kowal, and R.W. De Doncker, “Circuit breaker concepts for future high-power  dc-applications,” in Proc. IEEE Ind. Appl. Soc. Conf., 2005, vol. 2, pp. 860–866.

[5] Maqsood and K. A. Corzine, “Z-source breakers with coupled inductors,” presented at the IEEE Energy Conversion Congress Expo.,Montreal, Canada, Sep. 2015.

[6] J. Magnusson, R. Saers, and L. Liljestrand, “The commutation booster, a new concept to aid commutation in hybrid dc-breakers,” presented at the Cigr´e Symp. HVDC, Lund, Sweden, May 2015.

[7] Y. Liu, X. Wei, C. Gao, and J. Cao, “Topological analysis of HVDC circuit breaker with coupling transformer,” in Proc. IEEE Int. Conf. DC Microgrids, Jun. 2015, pp. 129–134.

[8] K. A. Corzine, “Circuit breaker for dc micro grids,” in Proc. IEEE Int.

Conf. DC Microgrids, Jun. 2015, pp. 221–221c.

[8] Power Systems: J. B. Gupta.

[9] Power Systems: A. Chakrabarti, Soni MI, P. V. Gupta.

[10] R. Cuzner, D. MacFarlin, D. Clinger, M. Rumney, and G.Castles, “Circuit breaker protection considerations in power converter fed dc systems,” in Proc. IEEE Electro. Ship

Technol. Symp., Apr. 2009, pp. 360–367

[11] Kempkes, M.; Roth, I.; Gaudreau, M., “Solid-state circuit breakers for Medium Voltage DC power,” Electric Ship Technologies Symposium (ESTS), 2011 IEEE , vol., no., pp.254,257, 10-13 April 2011

[12] Corzine, K.A.; Ashton, R.W., “A New Z-Source DC Circuit Breaker,” Power Electronics, IEEE Transactions on , vol.27, no.6, pp.2796-2804,June 2012