AU708569B3 - Induction of power (in motor) from a stationary object (stator) to a rotary object (rotor) with automatic and sensorless speed and position detection - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE APPLICATION PETTY PATENT INDUCTION OF POWER (INA MOTOR) FROM A STATIONARY OBJECT (STA TOR) TO A ROTARY OBJECT (ROTOR) WITHA UTOMA TIC AND SENSORLESS SPEED AND POSITION DETECTION This invention was made from the personal experience of the main applicant in the field and the result of his studies under the supervision of the co-inventors at Victoria University of Technology, Melbourne, Australia.

This document is a complete description of this invention and includes a total of 13 pages (including this page), 7 figures in five pages and an abstract at the end of the document.

Signature...... Ho 55re/ MAHQAY'4-A, Date...3o...

INTRODUCTION:

This invention improves the performance of a system in which traditionally a moving part extracts power from a stationary supply by means of brushes. In this invention a method is used to induce power from a stationary object to a rotary object with no physical contact between the stationary and rotary parts. In particular, the application of this method is advantageous in electrical motors with permanent magnet in the construction of their rotor. These motors can be brushless permanent magnet motors or brushed permanent magnet motors. Brushed permanent magnet motors have maintenance problems due to brushes and commutator wearing out and these motors also generate high levels of electromagnetic interferences (EMI). Brushless permanent magnet motors have expensive permanent magnets and due to the constant air-gap flux these motors have deficiencies at high-speed operation. Besides, brushless permanent magnet motors require a mechanism for position detection of the rotor with respect to the stator poles in order to change the polarity of the stator field when each time opposite polarities rotor and stator magnetic fields are reached due to rotor rotation. This invention provides a means of sensorless speed and position detection that is inherent in the design with no extra position detection modules as traditionally is being used in industry. This inherent characteristic is used to generate commutation pulses for stator winding with no external position detection module.

In terms of inducing power from a rotary object to a stationary object, similar works (like US patent 5691687) have been sited by our search through patent database. However, these works lack many fundamental advantages that our invention offers.

These advantages are: Use of HF switching to reduce the size of the main power transferring part (ie.

transformer).

Use of resonance to increase the power levels that can be transferred from the stationary object (stator) to the rotary (rotor) object.

Use of a special transformer core shape to induce power and to detect the position and the speed of the rotary object (rotor) and to generate the commutation control pulses of stator winding with no position sensors.

Reduction in EMI due to the use of resonant driving circuit.

These advantages will be the basis of our claims for our invention and will be described in the section "We claim:" DESCRIPTION OF THE INVENTION: Figure 1 illustrates the block diagram of the invention and the construction of the motor.

The subsections of the invention described hereafter can be best understood by referring to Figure 1 and the figures and details of the paragraphs titled by the subsections.

Section 8 consists of a resonant switch mode power supply that supplies the power to the motor and its associated electronics including the driving ac voltage for the primary of transformer 3.1. Transformer 3 is the main section where the power from a stationary object 3.1 is induced to a secondary object 3.2. The secondary of the transformer 3.2 is separated from primary 3.1 with a distance of 0.5-1 mm. Due to the separation of primary 3.1 and secondary 3.2 cores and windings, the leakage inductance is high. To counter the leakage inductance effect, the switch mode power supply 8 consists of a capacitance in series with the primary of the transformer 3.1 winding. This results in neutralisation of the leakage inductance and increases the power delivery to the secondary winding 3.2.

The frequency of operation of the driving pulse to the transformer is about 40-50kHz for our prototype but a frequency of 20-500kHz is practical. Secondary side of the transformer 3.2 is attached to the rotor and through the slot of rotor shaft 2.2, the secondary winding of 3.2 is connected to the rectifier 6 on the rotor 2. The rectifier 6 converts the ac voltage to de voltage. The output dc voltage of the rectifier section 6 is connected to the rotor winding 2.1. This voltage generates a static magnetic field similar to magnetic field of a permanent magnet. The stator winding 1.1 is driven by the driver section 5 which can be single or multiple phase similar to a permanent magnet brushless motor. The high frequency transformer 3 consists of ferrite cores from RM series of Philips Co. or similar. Figure 2 illustrate the core shape. When the rotor 2 is in a position in which the stationary core of the transformer 3.1 is in alignment (0 degree angular position) with the rotary section 3.2 (Figure the current of the primary of the transformer 3.1 reaches a minimum value because of the lower magnetisation current of the transformer primary 3.1. When the rotor 2 is in a position in which the stationary core of the transformer 3.1 is perpendicular (90 degree angular position) to the rotary section 3.2 (Figure the primary current of the transformer 3.1 reaches a maximum value because of higher magnetisation current of the transformer primary 3.1. At any other position between 0 and 90 degree angular alignment of the stationary part 3.1 and the rotary part 3.2, a value of the current in primary of transformer 3.1 is reached which is between the said maximum and minimum of the current. When the rotor 2 rotates, this current changes between the said maximum and minimum. By measuring the current of primary 3.1 (section 7 and section the position of rotor 2 with respect to stator 1 is calculated. From the rate of change of minimum or maximum of the current of primary 3. I, the speed of the rotor is calculated by section 4.

17-143 Current detection circuit 7 performs signal conditioning on the primary transformer 3.1 current. Section 7, consists of a current transducer, a peak detector section, and an amplification-filtering section. DSP data acquisition section 4 processes the output of section 7 to determine its maximum and minimum values in real-time and to find the angular position of the rotor 2 with respect to stator. Control pulses are generated at section 4 for commutation of the stator winding drive of section 5. A closed loop speed and/or position control system is implemented by the DSP section. The construction of the motor was described in previous section. In the following paragraphs the details of Section 3 to Section 8 are described.

SECTION 3: The parameters of HF transformer of our prototype which its model is illustrated in Figure 3 are: Rs Equivalent series resistance of primary and the secondary windings.

LL Equivalent leakage inductances of the primary and the secondary windings.

Lm(6) Equivalent magnetisation inductance of the primary as a function of rotor angular position 0.

n, Primary turns.

n2 Secondary turns.

Where: (Lnax-L,,in).[(7t-20)/7t] 0 0 7/2 LJEO) 1 -(Lmax-Lmin).[(7t-20)/t] +Lmi,, 7t/2 0 x and 3301H when 0 n/2 and Lin= 435H when 0=0 The cores are ferrite cores from Philips RM series.

SECTION 4: Section 4 is a general-purpose data acquisition board and DSP board. Our prototype utilises a TMS320C25 DSP board with 4 channels of ADC.

SECTION This section drives the stator winding with a single or multi-phase voltage. The simplified diagram of a typical drive system is illustrated in Figure 4. The drive system is similar to a standard permanent magnet drive system however no sensor for position detection is required.

SECTION 6: Section 6 consists of only a bridge rectifier with fast recovery diodes. The ac inputs of the rectifier are connected to the secondary winding of the transformer 3.2 and the de outputs of the rectifier are connected to the rotor winding 2.1. A filtering section can be added between the rectifier 6 and the rotor winding 2.2 to provide a filtered dc voltage to the winding. The rectifier and the optional filtering section of section 6 are mounted on the rotor 2 in such a way that symmetry is achieved in the plane perpendicular with the rotor shaft 2.2 and hence no unbalanced movement results due to the rotation of the components with rotor 2.

SECTION 7: The current detection circuit consists of a peak detector circuit similar to Figure 5. In this Figure: T1 is the HF transformer 3 D1 is rectifier of Section 6 RL is the dc resistance of the rotor winding 2.1 T2 is a current transformer sampling the current of the transformer T1 (primary winding of transformer 3.1) Circuit consisted of D2, R1, R2, C1 is the peak detector circuit that removes the switching current of the driving pulse form section 8 (high frequency portion) and only passes the low frequency voltage variations of the primary winding 3.1 current of the transformer T1 (HF transformer 3).

In section 7, there is also a dc amplifier with a variable dc bias. This dc amplifier amplifies the small variation of the primary winding transformer current 3.1 to increase the dynamic range of the signal for the section 4 where the position and speed data are extracted. At different mechanical loads of the motor and hence various rotor winding 2.1 current, the de offset at Vo in Figure 5 varies. This de offset is removed by the amplifier section and only the ac signal due to rotor 2 rotation is amplified. An ac coupled amplifier cannot be used for this purpose because the variation of the rotor winding 2.1 current can be random and the phase of the input and output of the amplifier must be constant at any load.

Figure 6 illustrates a typical voltage Vo for a given rotor winding 2.1 current.

SECTION 8: Section 8 consists of a resonant switch mode power supply. This section provides power for the control supply of Section 4, 5, and 7. Section 8 is the main supplier of power to the HF transformer 3. Due to the high leakage inductance of the transformer 3 (LL in Figure a resonant capacitor is used in series with the transformer 3.1 leakage inductance LL with the switching frequency of the power supply as the resonant frequency. Figure 7 illustrates the output stage of the power supply connection to the HF transformer 3.

In Figure 7, the resonant capacitor is 47nF, the leakage inductance is 300 1 H and the resonant frequency (Section 8 power supply switching frequency) is about 42kHz.

Except from the output stage of the power supply of Section 8, this power supply is similar to standard switching power supplies. The type of topology of the power supply is preferably half-bridge or full-bridge but any other topology that can neutralise the effect of leakage inductance LL with resonance can be used. Section 8 hence includes subsections standard for switching power supplies. This subsections are like EMI filtering and isolation between primary and secondaries.

Claims (4)

1. A motor and a motor drive system with a wound rotor on rotor shaft, the system comprising: a) a high frequency ferrite transformer with its primary attached to the stator chassis and supplied by a magnetisation current and a secondary winding being mounted on the rotor shaft for rotation therewith; b) a resonant switch mode power supply, said power supply being connected to the primary winding of the transformer with a capacitor in series, where the capacitor is in resonant with the leakage inductance of the transformer; c) a rectifier mounted on the rotor shaft for rotation therewith, and rectifying the output of the transformer secondary winding voltage to produce a dc voltage to supply the rotor windings; wherein the cores of the primary and secondary of the transformer are shaped in such a way that the rotation of the rotor and hence the two cores changes the magnetisation current of the primary winding of the transformer, this change in current being amplified and used to detect the position of the rotor.

2. The motor drive system of claim 1 wherein the speed and position of the rotor is detected with no sensor and by amplification of the variation in the magnetisation current of the high frequency transformer described in claim 1.

3. The motor drive system of claim 1 wherein the commutation pulses of the stator winding is generated with no sensor and by amplification of the variation in magnetisation current of the high frequency transformer described in claim 1. Signature Date..3.. Q.

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