ELECTRONIC BRAKING AND ENERGY RECYCLING SYSTEM ASSOCIATED WITH DC BRUSHLESS MOTOR

Abstract

An electronic braking and energy recycling system associated with a direct current (DC) brushless motor, characterized in that when an electronic braking task is launched, a phase voltage occurred in an inverse mode is applied onto a motor coil corresponding thereto and a gate voltage signal with positive and negative cycles is used to control an upper-side and lower-side branches to switch as compared to each other in the system, so as to redirect a current flown through the motor back to a power source end. In this invention, a controllable inverse torsion is achieved, enabling an electrical machine to be braked smoothly and reliably when necessary. As such, a dynamic power of the motor can be recycled at a maximum rate and thus the purpose of energy recycling is achieved. In addition, no complex circuitry configuration owing to the multi-phase coils is required.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings disclose illustrative embodiments of the present invention which serve to exemplify the various advantages and objects hereof, and are as follows:

FIG. 1 is a schematic diagram illustrating a current occurred when a dynamic power is derived from a prior art direct current (DC) brush controller;

FIG. 2 is a schematic diagram illustrating how an inverse torsion is outputted from the DC brush controller when operated under a high speed by switching a direction of the current with a lower-side thereof;

FIG. 3 is a schematic diagram illustrating how an upper-side branch of the DC brush controller is used to switch the direction of the current when operated at a low speed;

FIG. 4 is a schematic diagram of the direction of the current occurred when the dynamic power is derived from the DC brush controller (another two phases both correspond to a cut-off state);

FIG. 5 is a schematic diagram illustrating how the lower-side branch of the DC brush controller is used to switch the direction of the current when operated under a high speed;

FIG. 6 is a schematic diagram illustrating how the upper-side branch of the DC brush controller is used to switch the direction of the current when operated at a low speed according to the present invention;

FIG. 7 is a schematic diagram illustrating how an upper and lower-side branches are inversely switched to control the direction of the current according to the present invention;

FIG. 8 is a schematic diagram illustrating how the DC brushless controller operates when the upper and lower-side branches are inversely switched, considering currents on three phases according to the present invention;

FIG. 9 is a schematic diagram illustrating how the electronic braking control is achieved by using simple gate array logics according to an embodiment of the present invention; and

FIG. 10 is a schematic diagram of a current waveform as recycled obtained from the above embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses an electronic braking and energy recycling system associated with DC brushless motor, which can provide an inverse torsion-based braking function by using a conversion of a gate voltages under the condition without altering the conventional motor controller and any hardware configuration of the motor. Further, the inventive system can achieve the maximum recycling ratio for the dynamic power of the motor without being interfered with the multi-phase coil.

Referring to FIG. 7, the DC brushless motor is shown therein, in which a current is shown as flowing through a coil of the motor with the flow direction thereof also indicated. When the electronic braking system is launched, a controller applies a voltage associated with an inverse mode onto the indicated motor coil. At this time, the current flown through the motor coil has the relationship with other parameters related to the motor (Voltage-Time Law: V_motor×Δt_ON=L_motor×Δi_motor):

(ε_motor+V_source)×Δt_ON=L_motor×Δi_motor  (1)

As compared to the prior art, the only difference is that a MOSFET on a lower-side branch at the left part is not always maintained in “ON” status. Instead, the mentioned MOSFET on the lower-side branch is operated in a synchronous switching state with a MOSFET on an upper-side branch at the right part. In this manner, the current flown through the motor coil can be redirected back to a power end as the MOSFETs of the upper and lower-side branches are turned off.

In the case of an electrical machine operating in a high speed or a system requiring a small torsion, when it is braked, the motor coil restores the current flown therethrough back to a zero-current state. That is, the electrical machine or system is operated in the so-called “zero-current switching state”. In the turn-off cycle, the Voltage-Time Law is:

V _source ×Δt _→Zero =L _motor ×Δi _motor  (2)

Since the current is each time restored back to the zero-current state, a ratio of the turn-on time to the turn-off time can be represented as:

$\begin{array}{cc}\frac{\Delta t_{\mathrm{ON}}}{\Delta t_{\to \mathrm{Zero}}}=\frac{V_{\mathrm{source}}}{\left(V_{\mathrm{source}}+{\varepsilon }_{\mathrm{motor}}\right)}.& \left(3\right)\end{array}$

On the other hand, since an electrical power consumption associated with the current i is 0.5×V_source×Δi_motor×Δt, a ratio of recycled energy recycling to supplied energy is:

$\begin{array}{cc}\frac{\left(V_{\mathrm{source}}+{\varepsilon }_{\mathrm{motor}}\right)}{\left(V_{\mathrm{source}}\right)}=1+\frac{{\varepsilon }_{\mathrm{motor}}}{V_{\mathrm{source}}}.& \left(4\right)\end{array}$

In the case of an electrical machine operating in a low speed or a system requiring a large torsion, when it is braked, the motor coil enters a continuous state rather than the zero-current state. At this time, a duty time of the braking task is:

Duty=Δt_ON/(Δt_ON+Δt_OFF)  (5)

and the Voltage-Time Law is then:

(ε_motor+V_source)×Duty×Δt=L_motor×Δi_motor  (6)

and

(ε_motor−V_source)×(1−Duty)×Δt=L_motor×Δi_motor  (7)

Under momentary consideration, since a variation of the current in each cycle is approached to zero, the duty time can be rewritten as:

$\begin{array}{cc}\mathrm{Duty}\approx \frac{\left(V_{\mathrm{source}}-{\varepsilon }_{\mathrm{motor}}\right)}{2\times V_{{\mathrm{source}}_{25}}},\mathrm{and}& \left(8\right)\\ \left(1-\mathrm{Duty}\right)\approx \frac{\left(V_{\mathrm{source}}+{\varepsilon }_{\mathrm{motor}}\right)}{2\times V_{\mathrm{source}}}.& \left(9\right)\end{array}$

At this time, the electrical power is the same as that associated with the above case 0.5×V_source×Δi_motor×Δt. Accordingly, the ratio of recycled energy and supplied energy is:

$\begin{array}{cc}\frac{\left(V_{\mathrm{source}}+{\varepsilon }_{\mathrm{motor}}\right)}{\left(V_{\mathrm{source}}-{\varepsilon }_{\mathrm{motor}}\right)}=1+\frac{2\times {\varepsilon }_{\mathrm{motor}}}{\left(V_{\mathrm{source}}-{\varepsilon }_{\mathrm{motor}}\right)}.& \left(10\right)\end{array}$

According to Eqs. (4) and (10), the ratio of recycled energy and supplied energy is certainly greater than one and considerably increases as the induced electromotive force increases, meaning that such electronic braking mechanism truly provides an energy recycling function without the problem of electrical loss resulting from the braking task.

In a rotating brushless motor, there are six possible sets of coil phases (positive and negative voltages) relationships, including the one shown in FIG. 8. As shown in FIG. 8, since the upper-side branch at the right end and the lower-side branch at the left end switch synchronously, the induced voltages of the other two coils do not affect the operation of the control mechanism.

Referring to FIG. 9, in which the electronic braking and energy recycling system according to an embodiment of the present invention is depicted. As shown in FIG. 9, the system embodiment is a simple example of use thereof. The basic structure of this embodiment is obtained from the patents TW251395 and U.S. Pat. No. 6,960,896, except that the braking function is implemented by the signals for emergent stop used in these two patents. Logic gate 1 (gate array logic, GAL) is here used for signal decoding. Logic gate 1 is also used to provide accurate phase signals associated with the three-phase upper and lower-side branches when a braking signal is inputted. A micro-control unit 2 is configured to converse a torsion command into a current command and monitor a safety issue of the system by using a power control technology. A simple shunt is use to converse the current signal into a voltage signal. This voltage signal is then amplified and transmitted to a comparator 3. Finally, an output from the comparator 3 is forwarded to a current mode pulse width modulation (PWM) controller, ST3842, 4, in which the output from the comparator 3 is served as a reference for a PWM process.

FIG. 10 is a schematic diagram of a current waveform as recycled obtained from the embodiment shown in FIG. 9. In this drawing, the positive current means the current is flowed from the power source to the electrical system and thus an energy output, while the negative current means the current is flowed from the electrical system to the power source and this an energy recycling. It can be appreciated that the proportion of the energy recycling is almost a constant value when the motor rotates at a constant speed.

These variations, modifications, alternatives, and alterations of the various preferred embodiments, arrangements, and configurations may be used alone or in combination with one another as will become more readily apparent to those with skill in the art with reference to the following detailed description of the preferred embodiments and the accompanying figures and drawings.

Numerous alterations, modifications, and variations of the preferred embodiments disclosed herein will be apparent to those skilled in the art and they are all anticipated and contemplated to be within the spirit and scope of the instant invention. For example, although specific embodiments have been described in detail, those with skill in the art will understand that the preceding embodiments and variations can be modified to incorporate various types of substitute and or additional or alternative materials, relative arrangement of elements, and dimensional configurations. Accordingly, even though only few variations of the present invention are described herein, it is to be understood that the practice of such additional modifications and variations and the equivalents thereof, are within the spirit and scope of the invention as defined in the following claims.

Claims

1. An electronic braking and energy recycling system associated with a DC brushless motor, characterized in that when an electronic braking task is launched, a phase voltage occurred in an inverse mode is applied onto a motor coil corresponding thereto and a gate voltage signal with positive and negative cycles is used to control an upper-side and lower-side branches to switch, so as to redirect a current flown through the motor back to a power source end.

2. The electronic braking and energy recycling system as claimed in claim 1, wherein the gate voltage is applied onto a set of respective MOSFETs on the upper and lower-side branches to switch as compared to each other synchronously.