摘要:
A pulse-width modulated (PWM) circuit applies a voltage across a load (32) in accordance with a PWM command signal (I). The command signal (I) is converted into first and second trains of pulses (x, x'), by electronically comparing the command signal with a triangular dither signal (D) and also with the dither signal which has been shifted by half its period. These two pulse trains, and two more pulse trains (y, y) obtained by taking the complements of the original pulse trains, are applied to a pair of bridge circuits (A, B). The load (32) is connected to both bridge circuits. Both bridge circuits are configured such that when a pulse is present, from either the first or the second pulse train, no net voltage appears across the load. At all other times, substantially the entire power supply voltage is applied across the load. In another embodiment, n pairs of bridge circuits are connected across the load. The pulse trains are generated using dither signals which are shifted in time. The pulse trains of one pair of bridge circuits are shifted from the next pair by t/2n, where t is the period of the dither signal. The greater n, the less the effective ripple current in the load. The invention is especially suitable for use in controlling gradient coils in a magnetic resonance imaging system.
摘要:
A high-speed constant-horsepower motor includes a rotor and a stator having a plurality of groups of windings which are separately driven. In one mode of operation, the polarity of the voltage applied to each winding is such that the windings behave as distinct electromagnets, each defining a separate magnetic pole. In another mode of operation, the polarity of voltage applied to some of the windings is reversed, such that pairs of adjacent windings behave as single electromagnets. In the latter mode, the effective number of magnetic poles is reduced by a factor of two. Thus, the effective number of magnetic poles of the motor can be varied electronically, even while the motor is operating. The invention makes it possible, in one example, to operate the motor as an eight-pole motor at low speeds, and as a four-pole motor at high speeds. The effective motor constants are changed appropriately from eight-pole to four-pole modes. The invention also includes a circuit which minimizes the number of slip rings (50, 51), or other power transferring devices, required to implement the above-described invention on the windings of the rotor.
摘要:
A pulse-width modulated (PWM) circuit applies a voltage across a load (32) in accordance with a PWM command signal (I). The command signal (I) is converted into first and second trains of pulses (x, x'), by electronically comparing the command signal with a triangular dither signal (D) and also with the dither signal which has been shifted by half its period. These two pulse trains, and two more pulse trains (y, y) obtained by taking the complements of the original pulse trains, are applied to a pair of bridge circuits (A, B). The load (32) is connected to both bridge circuits. Both bridge circuits are configured such that when a pulse is present, from either the first or the second pulse train, no net voltage appears across the load. At all other times, substantially the entire power supply voltage is applied across the load. In another embodiment, n pairs of bridge circuits are connected across the load. The pulse trains are generated using dither signals which are shifted in time. The pulse trains of one pair of bridge circuits are shifted from the next pair by t/2n, where t is the period of the dither signal. The greater n, the less the effective ripple current in the load. The invention is especially suitable for use in controlling gradient coils in a magnetic resonance imaging system.
摘要:
A pulse-width modulated circuit applies a voltage (+V) across a load (32) in accordance with a command signal (I). The command signal is converted into first and second trains of pulses (x, x′), by electronically comparing the command signal, and its inverse, with a triangular dither signal (38). These two pulse trains (x, x′), and two more pulse trains ( y , y′) obtained by taking the complements of the original pulse trains, are applied to a pair of bridge circuits (48, 50). The load is connected to both bridge circuits. Both bridge circuits include electronic switching devices (60, 62, 64, 66, 68, 70, 72, 74) actuated by the pulses. The bridge circuits are configured such that when a pulse is present, from either the first or the second pulse train, no net voltage appears across the load. At all other times, substantially the entire power supply voltage is applied across the load. Compared to pulse-width modulated circuits of the prior art, having similar pulse frequencies and power supplies, the present circuit reduces the undesirable effects of current ripple through the load by a factor of four. This reduction is due to the use of two alternating pulse trains, which doubles the effective frequency of pulses, and to the fact that the maximum voltage excursion of the signal across the load is no greater than the absolute value of the maximum power supply voltage available. As a result, the present circuit has a much higher bandwidth than circuits of the prior art having comparable voltage and frequency parameters.
摘要:
An apparatus for use with an amplifier (51-56) regulates the current through a load (35) according to a drive signal (93) having first and second states and comprises switchless sensing means (62, 64) and polarity correction means (66, 68). The switchless sensing means (62, 64) provides a sense signal continuously representative of the magnitude of the current through the load (35) without the use of switching circuitry. The polarity correction means is directly coupled to the sensing means (62, 64) and receives the sense signal and is responsive to the status of the drive signal (93) for providing an analog signal (102) continuously representative of both the instantaneous magnitude and polarity of the current through the load.
摘要:
Analog sensors generate phase-displaced analog signals responsive to the angular position of a shaft. A logic circuit (12) produces a digital code indicating the region of the cycle in which the shaft is instantaneously located. An analog multiplexor (14) selects a unique pair of analog signals according to the value of the digital code. An analog to digital converter (16, 26) then generates a digital signal used to activate an address in a memory (28). As the shaft turns, the addresses in the memory (28) are activated in a predetermined order to produce trains of pulses indicating angular velocity, direction as well as displacement of the shaft, and commutation pulses, for controlling a brushless motor. The apparatus therefore can be used to monitor the angular displacement of the shaft and, at the same time, to control the motor which drives that shaft.
摘要:
Analog sensors generate phase-displaced analog signals responsive to the angular position of a shaft. A logic circuit (12) produces a digital code indicating the region of the cycle in which the shaft is instantaneously located. An analog multiplexor (14) selects a unique pair of analog signals according to the value of the digital code. An analog to digital converter (16, 26) then generates a digital signal used to activate an address in a memory (28). As the shaft turns, the addresses in the memory (28) are activated in a predetermined order to produce trains of pulses indicating angular velocity, direction as well as displacement of the shaft, and commutation pulses, for controlling a brushless motor. The apparatus therefore can be used to monitor the angular displacement of the shaft and, at the same time, to control the motor which drives that shaft.
摘要:
A pulse-width modulated circuit applies a voltage (+V) across a load (32) in accordance with a command signal (I). The command signal is converted into first and second trains of pulses (x, x′), by electronically comparing the command signal, and its inverse, with a triangular dither signal (38). These two pulse trains (x, x′), and two more pulse trains ( y , y′) obtained by taking the complements of the original pulse trains, are applied to a pair of bridge circuits (48, 50). The load is connected to both bridge circuits. Both bridge circuits include electronic switching devices (60, 62, 64, 66, 68, 70, 72, 74) actuated by the pulses. The bridge circuits are configured such that when a pulse is present, from either the first or the second pulse train, no net voltage appears across the load. At all other times, substantially the entire power supply voltage is applied across the load. Compared to pulse-width modulated circuits of the prior art, having similar pulse frequencies and power supplies, the present circuit reduces the undesirable effects of current ripple through the load by a factor of four. This reduction is due to the use of two alternating pulse trains, which doubles the effective frequency of pulses, and to the fact that the maximum voltage excursion of the signal across the load is no greater than the absolute value of the maximum power supply voltage available. As a result, the present circuit has a much higher bandwidth than circuits of the prior art having comparable voltage and frequency parameters.