An Integrated Multi-Port Power Converter with Small Capacitance Requirement for Switch Reluctance Machine

Transcription

1 Renewable Energy and Vehicular Technology Lab An Integrated Multi-Port Power Converter with Small Capacitance Requirement for Switch Reluctance Machine Wen Cai, Fan Yi, Lei Gu and Babak Fahimi October 30, 2014 Some pictures are from

2 Contents Introduction Topology analysis Corresponding control methods Simulation & experimental results Conclusion & future work 2014/11/3 2

3 1. Introduction Power fluctuation in SRM drive i Current commutation Phase a Phase b Phase c S3 D2 S5 D4 S7 D6 V1 C p t D1 S4 D3 S6 D5 S8 Phase a Phase b Phase c power ripple 2014/11/3 3 t SRM Conventional asymmetrical SRM drive 1) Large electrolytic capacitor is necessary on the dc bus; 2) There are 6 switches and 6 diodes in the SRM drive; 3) DC bus voltage must be high enough;

4 1. Introduction Why should we reduce capacitance? Large capacitance(6800uf) Voltage limitation(450v) Expensive Short Lifetime electrolytic capacitor Theoretical lifetime of electrolytic capacitor is only about 30,000h at high operating temperature(85ºc) $60.0 $180.0 $7.9 $23.7 $4.8 $9.6 Data from Long lifetime High voltage(1200v) Low ESR Small capacitance(20uf) film capacitor 2014/11/3 4 Reducing the capacitance can help to reduce the cost, the size and improve the lifetime.

5 1. Introduction How to reduce the capacitance requirement? In the current commutation period, ripple energy that C supplies is Eripple CU max CU min 2 2 C U U Constant Methods to reduce the capacitance: Enlarge the capacitor voltage ripple; Increase the capacitor average voltage; Voltage limitation In order to minimize the capacitor, voltage ripple must be enlarged. DC source Inverter SRM Input voltage should be constant The capacitor cannot be connected directly on the DC bus Constant power DC cap Alternating power 2014/11/3 5

6 Contents Introduction Topology analysis Corresponding control methods Simulation & experimental results Conclusion & future work 2014/11/3 6

7 2. Topology analysis Topology derivation for capacitance reduction Since the capacitor is not connected into the dc port any more, it can be treated as a source. Hence, there would be two dc sources in the power system which hints that the topology would be a multi-port converter, not a two-port DC-AC converter. V1 R S1 L S3 D2 S5 D4 S7 D6 C S2 D1 S4 D3 S6 D5 S8 Transient Power Unit Asymmetrical H-bridge 2014/11/3 7 Phase a Phase b Phase c A transient power unit is added in the previous converter. That unit is consists of one leg, an inductor as filter and the capacitor as buffer. SRM

8 2. Topology analysis Topology derivation for power decoupling of inverters Transient Power Unit Asymmetrical H-bridge V1 R S1 L S3 D2 S5 D4 S7 D6 Switch multiplexing technique C S2 D1 S4 D3 S6 D5 S8 Phase a Phase b Phase c SRM Requirements: 1) The voltage of the capacitor should be always higher than the dc source. 2) S 1 and S 2 should keep modulation continually. While, the other switches S 3, S 4 and S 5 would work alternatively. 3) The voltage stress of the switches is decided by the capacitor voltage directly. C R V1 S1 L S2 D1 S3 Phase a D2 D3 S4 S5 Phase b Phase c SRM 2014/11/3 8 Proposed topology in this paper

9 2. Topology analysis Compared with the conventional topology, the presented IMPC has some advantages listed as following: 1) The required capacitance could be reduced. The voltage ripple and average voltage of the capacitor can be increased. The lifetime of the SRM drive is improved. The cost and size can be optimized. 2) The number of the switches and diodes are decreased as well. The cost and size of the SRM drive can be optimized. 3) The range of the dc source voltage is expanded since it doesn t act as dc link. The dc source voltage can be low which is suitable for battery applications. 4) The dc link voltage is flexible. By increasing the dc link voltage, the time for discharging of each phase decreases so that conduction angle could be increased and larger average torque could be obtained. The power speed range is widened which is especially appealing for high speed application. 2014/11/3 9

10 Contents Introduction Topology analysis Corresponding control methods Simulation & experimental results Conclusion & future work 2014/11/3 10

11 3. Corresponding control methods Totally, there are two control loops: Input port control; Output port control; C R V1 S1 L D1 D2 D3 Input port control S2 S3 Phase a S4 Phase b S5 Phase c Capactor voltage control loop v cap_ref + - v cap PI i L_ref + - i L Inductor current control loop PI d 1 PWM generator g 1 g 2 SRM There are two control loops in input port control: capacitor voltage control(the outer one); inductor current control(the inner one); 2014/11/3 11 Explanation: inductor current reference is obtained by measuring the difference between the capacitor voltage and the detected value. The duty cycle of S 1 and S 2 is regulated according to the difference between the inductor current reference and the detected value.

12 3. Corresponding control methods Output port control C R S1 L D1 D2 D3 V1 Speed control loop Current control loop S2 S3 Phase a S4 Phase b S5 Phase c Speed_ref + - speed PI i abc_ref i abc Hysteresis Control g 3, g 4, g 5 SRM There are two control loops in output port control: speed control (the outer one); current control (the inner one); Explanation: the outer one is speed control which outputs the reference of the current injected into the motor. The inner one is current control and the three switches S 3, S 4 and S 5 are modulated here. Hysteresis control is used in consideration of that it is simple and easy to implement. 2014/11/3 12

13 Contents Introduction Topology analysis Corresponding control methods Simulation & experimental results Conclusion & future work 2014/11/3 13

14 4. Simulation & experimental results Simulation Asymmetrical H-bridge Parameter Value DC Voltage Source(V 1 ) 250V DC Capacitor Voltage(V c ) 250V DC, 20V AC Capacitor(C) 2000µF Integrated Multi-Port Converter DC Voltage Source(V 1 ) 250V DC Capacitor(C) 80µF Capacitor Voltage(V c ) 600V DC, 100V AC Inductor(L) 100µH, 10mΩ Switching frequency(fs) 20-kHz Switched Reluctance Machine Stator poles 6 Rotor poles 4 Te 40 Inertia 0.05kg.m.m Friction 0.02N.m.s Speed 1000RPM flux(v*s) Te(N*m) three-phase current(a) 2014/11/3 14 The steady-state simulation waveforms

15 4. Simulation & experimental results Simulation Input current(a) load torque change speed(rpm) [A] [Hz] ASHB IMPC 2014/11/3 Input current(a) 15 Harmonic distribution The control method can restrain 91% 100-Hz ripple component of the inverter input current

16 4. Simulation & experimental results Experimental results The experimental results are deleted by the author. 2014/11/3 16

17 Contents Introduction AC/DC three-port topology derivation Corresponding control methods Simulation & experimental results Conclusion & future work 2014/11/3 17

18 5. Conclusion & future work Conclusion: Proposed an integrated multi-port converter as SRM drive and analyzed its advantages especially capacitance requirement Achieved the topology modeling and designed the corresponding control methods to reduce the capacitance and drive SRM Verified the feasibility of the topology and the control methods by simulations and experiments Future work: To analyze the voltage and current stress and estimate the system efficiency To optimize the input current waveform with advanced control method 2014/11/3 18

19 2014/11/3 19