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The objective of this paper is to investigate the performance of 8/6 switched reluctance motor (SRM) when excited with sinusoidal voltage. The conventional R dump converter provides DC excitation with the help of capacitor. In this paper the converter used is the modified R dump converter without DC link capacitor providing AC or sinusoidal excitation. Torque ripple and speed ripple are investigated based on hysteresis current control. Constant and sinusoidal current references are considered for comparison in both DC and AC excitation. Extensive theoretical and experimental investigations are made to bring out the merits and demerits of AC versus DC excitation. It is shown that the constructionally simple SRM can be favorably controlled with simple R dump converter with direct AC excitation without need for DC link capacitor. A 4-phase 8/6 0.5 kW SRM is used for experimentation.

The switched reluctance motor (SRM) is the simplest and most efficient variable speed drive. It has high reliability and operates at very high speed. Generally SRM drives are excited with DC supply. AC voltage is rectified and smoothened by the DC link capacitor for DC excitation [

The single switch per phase converter like R dump, C dump [

The objective of this paper is to provide simple converter and control strategies for SRM to be operated with direct AC excitation with minimum number of switching devices and storage elements. SRM can be operated with bidirectional currents with direct AC excitation. This requires bidirectional switches increasing the complexity of the converter. Hence the configuration used in this paper for excitation is a full bridge diode rectifier followed by modified R dump converter without any capacitor at both the DC link and R dump circuit. This facilitates unidirectional sinusoidal excitation. Hysteresis current control is employed with DC and sinusoidal current references. Performance of the machine is analysed in terms of torque ripple, speed ripple, and total harmonic distortion (THD) at the input. Theoretical and experimental investigations are made and the relative merits and demerits of sinusoidal versus DC excitation are brought out.

This paper is organized as follows. Section

The conventional and modified R dump converters are shown in Figures

Conventional R dump converter for DC excitation.

Modified R dump converter for AC or sinusoidal excitation.

The performance of SRM is investigated with a full bridge rectifier and a utility AC supply which is shown in Figure

The functional block diagram of the proposer SRM drive is shown in Figure

Block diagram of SRM drive.

(a) Equivalent circuit of the incoming phase. (b) Equivalent circuit of the outgoing phase.

Figures

The simplest control for SRM can be the fixing of

The specification of the machine and the drive is given in Table

Switched reluctance motor, its hardware, and data acquisition specifications.

Motor specifications | Hardware configuration | Data acquisition specification | |||
---|---|---|---|---|---|

Rated power | 0.5 kW | Current sensor | LA-100P | DAQ board | NI PCI 6251 |

Rated current | 3 A | Voltage sensor | LV25-P | Real-time interface | Embedded target |

Stator poles | 8 | Optocoupler | MCT2E | Acquisition speed | 100 |

Rotor poles | 6 | MOSFET | IRFP450 | ||

Resistance/phase | 2.67 |
Diodes | IN4007 | ||

Capacitor | 1000 |

Performance of the SRM is analysed both theoretically and experimentally for two cases, namely, Case (i) DC and AC excitation with constant current reference and Case (ii) DC and AC excitation with sinusoidal current reference. The DC excitation considered in this paper is equivalent to the use of conventional R dump converter shown in Figure

Supply voltage and current of modified converter with constant current reference.

The phase currents and developed torque waveforms for the DC excitation are given in Figure

Phase currents and developed torque of SRM with 60 V DC excitation and constant current reference of 0.5 A.

Figure

Phase currents and developed torque of SRM with 60 V sinusoidal excitation and constant current reference of 0.5 A.

The values of average speed, speed ripple, average torque, and torque ripple are listed in Tables

Comparison of speed with DC and sinusoidal excitation with DC current reference.

Constant current |
Experimental analysis | Theoretical analysis | ||||||
---|---|---|---|---|---|---|---|---|

DC excitation (with capacitor) | Sinusoidal excitation (without capacitor) | DC excitation (with capacitor) | Sinusoidal excitation (without capacitor) | |||||

Average speed (RPM) | Speed ripple % | Average speed (RPM) | Speed ripple % | Average speed (RPM) | Speed ripple % | Average speed (RPM) | Speed ripple % | |

0.4 | 215 | 2.79 | 345 | 2.90 | 208 | 2.65 | 328 | 2.47 |

0.5 | 706 | 1.27 | 1829 | 1.20 | 659 | 1.17 | 1810 | 1.14 |

0.6 | 1518 | 0.46 | 2353 | 0.76 | 1478 | 0.41 | 2286 | 0.82 |

0.7 | 1973 | 0.35 | 2553 | 0.86 | 1952 | 0.32 | 2458 | 0.80 |

0.8 | 2307 | 1.52 | 2764 | 0.90 | 2295 | 1.57 | 2714 | 0.92 |

0.9 | 2469 | 0.81 | 2798 | 0.64 | 2423 | 0.88 | 2782 | 0.84 |

1.0 | 2510 | 0.84 | 2816 | 0.96 | 2498 | 0.85 | 2793 | 0.92 |

1.2 | 2620 | 0.88 | 2830 | 1.41 | 2601 | 0.83 | 2822 | 0.86 |

1.5 | 2934 | 1.29 | 2975 | 0.85 | 2896 | 0.81 | 2965 | 0.78 |

Comparison of torque with DC and sinusoidal excitation with DC current reference.

Constant current |
Experimental analysis | Theoretical analysis | ||||||
---|---|---|---|---|---|---|---|---|

DC excitation (with capacitor) | Sinusoidal excitation |
DC excitation |
Sinusoidal excitation | |||||

Torque average | Torque ripple % | Torque average | Torque ripple % | Torque average | Torque ripple % | Torque average | Torque ripple % | |

0.4 | 0.007 | 300.00 | 0.013 | 169.23 | 0.065 | 320.00 | 0.015 | 164.55 |

0.5 | 0.011 | 272.73 | 0.018 | 156.76 | 0.012 | 292.73 | 0.020 | 160.43 |

0.6 | 0.015 | 220.00 | 0.022 | 141.57 | 0.017 | 210.00 | 0.025 | 145.89 |

0.7 | 0.019 | 173.68 | 0.027 | 140.74 | 0.020 | 193.68 | 0.032 | 143.56 |

0.8 | 0.024 | 145.83 | 0.036 | 134.25 | 0.025 | 165.83 | 0.038 | 140.87 |

0.9 | 0.037 | 116.22 | 0.045 | 133.33 | 0.039 | 122.22 | 0.044 | 138.26 |

1.0 | 0.039 | 135.90 | 0.052 | 134.62 | 0.045 | 146.90 | 0.058 | 136.96 |

1.2 | 0.052 | 132.69 | 0.081 | 130.43 | 0.050 | 140.69 | 0.091 | 132.45 |

1.5 | 0.048 | 143.75 | 0.089 | 114.12 | 0.056 | 155.75 | 0.099 | 120.87 |

The SRM is tested for various current references, with different voltage magnitudes and the performance factors being tabulated. Table

100 V sinusoidal supply with different DC current references.

Constant current |
Average speed |
Speed ripple % | Torque ripple % | Power factor | THD for current |
---|---|---|---|---|---|

0.6 | 1283 | 4.45 | 85.51 | 0.44 | 89.2 |

0.7 | 1847 | 1.18 | 69.69 | 0.52 | 84.7 |

0.8 | 2110 | 1.21 | 47.06 | 0.57 | 82.1 |

0.9 | 2343 | 2.28 | 37.45 | 0.62 | 79.6 |

1 | 2520 | 2.08 | 32.46 | 0.64 | 76.9 |

1.2 | 2747 | 0.96 | 22.18 | 0.7 | 71.6 |

1.5 | 2797 | 0.79 | 16.32 | 0.75 | 65.3 |

By keeping a single DC current reference and varying the applied voltage the observed motor performance factors are tabulated in Table

1 A constant current reference with different voltage magnitudes.

Applied voltage | Average speed (RPM) | Speed ripple % | Torque ripple % | Power factor | THD for current |
---|---|---|---|---|---|

30 | 1364 | 0.86 | 61.6 | 0.814 | 55.9 |

60 | 1768 | 0.96 | 134.6 | 0.746 | 66.7 |

75 | 2301 | 1.23 | 142.2 | 0.684 | 72.4 |

100 | 2587 | 1.68 | 156.4 | 0.648 | 75.9 |

125 | 2827 | 1.94 | 172.4 | 0.616 | 77.9 |

150 | 2961 | 2.42 | 184.6 | 0.587 | 80.7 |

175 | 3261 | 2.76 | 192.6 | 0.572 | 81.3 |

200 | 3547 | 3.13 | 204.6 | 0.564 | 81.7 |

Supply voltage and current waveform of modified converter with sinusoidal current reference.

To reduce iron losses it is preferred to have the currents be sinusoidal. Hence the analysis is repeated with sinusoidal current reference at both DC and sinusoidal excitation. The phase currents and developed torque of the SRM, under sine current reference with conventional and modified converter, are shown in Figures

Phase currents and torque of SRM with 60 V DC excitation and sinusoidal current reference of 0.5 A.

Phase currents and torque of SRM with 60 V sinusoidal excitation and sinusoidal current reference of 0.5 A.

Tables

Comparison of speed with DC and sinusoidal excitation with sine current reference.

Sine current |
Experimental analysis | Theoretical analysis | ||||||
---|---|---|---|---|---|---|---|---|

DC excitation (with capacitor) | Sinusoidal excitation (without capacitor) | DC excitation (with capacitor) | Sinusoidal excitation (without capacitor) | |||||

Average speed (RPM) | Speed ripple % | Average speed (RPM) | Speed ripple % | Average speed (RPM) | Speed ripple % | Average speed (RPM) | Speed ripple % | |

0.4 | 315 | 6.79 | 445 | 4.90 | 332 | 6.43 | 462 | 5.60 |

0.5 | 816 | 4.27 | 1929 | 3.20 | 825 | 4.57 | 1935 | 3.70 |

0.6 | 1622 | 3.46 | 2453 | 1.76 | 1640 | 3.87 | 2420 | 1.86 |

0.7 | 2023 | 2.45 | 2753 | 0.86 | 2045 | 2.25 | 2732 | 0.76 |

0.8 | 2511 | 1.52 | 2864 | 0.90 | 2510 | 1.82 | 2837 | 0.80 |

0.9 | 2669 | 0.81 | 2898 | 0.64 | 2690 | 0.95 | 2878 | 0.74 |

1.0 | 2710 | 0.64 | 2916 | 0.66 | 2735 | 0.54 | 2903 | 0.65 |

1.2 | 2920 | 0.43 | 3254 | 0.41 | 2945 | 0.49 | 3276 | 0.48 |

1.5 | 3015 | 0.28 | 3685 | 0.25 | 3030 | 0.32 | 3665 | 0.29 |

Comparison of torque with DC and sinusoidal excitation with sine current reference.

Constant current reference (A) | Experimental analysis | Theoretical analysis | ||||||
---|---|---|---|---|---|---|---|---|

DC excitation (with capacitor) | Sinusoidal excitation (without capacitor) | DC excitation (with capacitor) | Sinusoidal excitation (without capacitor) | |||||

Torque average | Torque ripple % | Torque average | Torque ripple % | Torque average | Torque ripple % | Torque average | Torque ripple % | |

0.4 | 0.01 | 320.00 | 0.018 | 189.23 | 0.013 | 302.00 | 0.016 | 189.23 |

0.5 | 0.016 | 292.73 | 0.022 | 176.76 | 0.015 | 272.73 | 0.024 | 176.76 |

0.6 | 0.018 | 245.00 | 0.025 | 161.57 | 0.019 | 255.00 | 0.026 | 161.57 |

0.7 | 0.021 | 203.68 | 0.027 | 150.74 | 0.023 | 223.28 | 0.028 | 150.74 |

0.8 | 0.026 | 165.83 | 0.039 | 144.25 | 0.029 | 155.38 | 0.043 | 144.25 |

0.9 | 0.037 | 136.22 | 0.045 | 133.33 | 0.040 | 127.73 | 0.049 | 133.33 |

1.0 | 0.041 | 125.90 | 0.057 | 122.62 | 0.046 | 112.45 | 0.061 | 122.62 |

1.2 | 0.046 | 102.69 | 0.085 | 100.43 | 0.049 | 99.86 | 0.082 | 100.43 |

1.5 | 0.048 | 83.75 | 0.089 | 88.12 | 0.052 | 76.88 | 0.093 | 88.12 |

The machine performance based on power factor and THD is also obtained by exciting it with 100 V supply and various current references which are tabulated in Table

100 V sinusoidal supply with various constant current references.

Sine current |
Average speed (RPM) | Speed ripple % | Torque ripple % | Power factor | THD for current % |
---|---|---|---|---|---|

0.6 | 2385 | 6.45 | 185.25 | 0.74 | 69.2 |

0.7 | 2567 | 4.19 | 169.69 | 0.78 | 64.7 |

0.8 | 2683 | 3.23 | 147.16 | 0.81 | 52.1 |

0.9 | 2891 | 2.78 | 137.25 | 0.83 | 48.6 |

1 | 3245 | 2.38 | 132.86 | 0.85 | 39.9 |

1.2 | 3675 | 1.96 | 122.28 | 0.87 | 35.6 |

1.5 | 3797 | 1.79 | 116.32 | 0.92 | 32.3 |

The supply current is highly distorted due to the switching of the converter switches. Because of this the power factor is becoming poor and produces high harmonics. The supply current contains only third harmonics; hence lower iron loss is expected. The phase current waveform for a constant current reference of 0.5 A is shown in Figure

Phase currents for 0.5 A reference 60 V DC.

Phase B current waveform for 0.5 A reference 60 V DC.

The rating of transistor

Control part is organized through hardware in loop model. Commutations pulses are generated based on the information from position sensor which is acquired through a National Instrumentations Data Acquisition (NI DAQ) card PCI 6251. An R dump converter with necessary isolation and gate drivers are used to commutate the phase current. Hall effect current and voltage sensors are used for measuring the active phase voltage and current, respectively.

Hardware implementation of the modified R dump converter and its components are shown in Figures

DAQ terminator, R dump converter, 8/6 SRM, and sensors.

Hardware of modified R dump converter.

The electromagnetic performance of an 8/6 SRM with DC and sinusoidal excitation is investigated in terms of torque capability, torque ripple, average speed, and speed ripple. The standard single phase full bridge is employed to make unidirectional current flow in SRM phases. The DC link capacitance is removed which makes the converter weigh less and be cost effective. Lower torque and speed are observed in DC excitation. The iron loss with sinusoidal excitation is significantly reduced due to less current harmonics at high current reference. Thus the efficiency will be high at high speed. The modified converter can be used for fan type loads.

The authors declare that there is no conflict of interests regarding the publication of this paper.