KR20140056006A - System and method for controlling an electric motor - Google Patents

Abstract

A system (100) for controlling an electric motor (112), based on N-MOS switching device (116), allows operation in direct battery polarity condition and protects the switching device (116) against voltage peaks when in direct battery polarity condition. The system (100) includes a power source (114), a switching device (116) connected in series with the motor (112) to switch the motor (112) between ″on″ and ″off″ states, a control device (118) to control the switching device (116), and a thyristor (124) connected in parallel with the motor (112), thereby controlling a current conducting or non-conducting state of the thyristor (124) by the control device (119). Also, a method (200) provided for controlling an electric motor (112) such as in a system (100) described above, comprises: a step (210) of switching a state of the thyristor (124) in direct battery polarity conditions such that the thyristor conducts current; and switching the state of the thyristor in reverse battery polarity conditions such that the thyristor does not conduct current.

Description

TECHNICAL FIELD [0001] The present invention relates to a system and a method for controlling an electric motor,

The present invention relates to an electro-electronic circuit comprising a solid-state relay (SSR). More particularly, the present invention relates to an electronic circuit including an SSR for controlling a DC motor.

Electromechanical relays are widely known in the field and are widely used in various types of power control and electrical applications. These mechanical devices, which generally include coils and contacts, are highly reliable despite the problems involved with the presence of moving parts. Mechanical relays are also susceptible to electrical sparking and arcing.

Mechanical relays also generate abrupt phase transitions between "on" and " off "states, producing high current peaks in the circuit at each phase transition. Such current peaks, for example, cause melting of the contacts of the circuit, resulting in malfunction of the electrical system.

Today, solid state relays (SSRs) are used as alternatives to electromechanical relays in a variety of applications, including automotive electronics applications for the control of direct current motors. Numerous advantages of SSR compared to mechanical devices can be noted. Numerous advantages include improved overcurrent control, reduced size and weight, better power dissipation, and higher operating frequency.

However, in this application, it can be seen that SSR has the disadvantage that when compared to an electromechanical relay, an external reverse battery polarity protection circuit is required when the polarity of the power source is opposite.

The most commonly used solutions for protection against polarity inversion are:

(I) using diodes in series with power lines; However, given the power dissipation, this technique can only be applied to low current systems.

(Ii) using diodes in series with electro-mechanical relays capable of switching power lines on and off. However, the use of such switching devices involves all the problems inherent in electro-mechanical relays as described herein.

(Iii) using P-channel MOSFETs to switch power lines. However, this solution entails a power loss problem due to the high junction resistance of the P-channel device. In addition, such devices are limited to use in relatively low current circuits.

An N-channel MOSFET (N-MOS) device for switching the motor can be further employed. However, such devices do not receive any protection against reverse voltage peaks when operating with direct battery polarity (e.g., when the motor is off). Thus, the power is lost by the N-MOS device and causes its overheating.

Since the reverse voltage peak is lost without damaging the N-MOS device, a diode connected in parallel with the motor will solve this problem. However, in the battery reverse polarity state, the diodes will cause current to flow directly to the N-MOS device without going through the motor, thereby damaging the N-MOS device.

Therefore, there is a need for an element that can eliminate the above disadvantages.

The subject matter discussed in the Background section should not be construed as prior art as a result of merely mentioning in the Background section. Likewise, the problems associated with the subject matter of the background section referred to in the background section should not be regarded as presently recognized in the prior art. The subject matter of the background art, however, represents a different approach that can be invented on its own merely by itself.

It is a first object of the present invention to provide a method and system for the control of an electric motor based on an N-MOS switching device and to operate it in a reverse polarity state of the battery.

A second object of the present invention is to provide a method and apparatus for protecting an electric motor based on an N-MOS switching device against a reverse voltage peak generated by switching of an electric motor in a system using PWM and preventing power loss in an N-MOS device , Thereby providing a method and system for controlling it to prevent its overheating.

In order to achieve the above object, the present invention provides a system for controlling an electric motor comprising a switching device connected in series with a motor for switching between a power source, a motor, and an "off" And a thyristor connected in parallel with the motor, the gate terminal of the thyristor, and consequently its current conduction or non-conduction state, is controlled by the control device.

The invention also provides a method of controlling an electric motor in a system as defined above, the method comprising: switching the phase of the thyristor to a battery positive state so that the thyristor conducts current; So as to switch the phase of the thyristor to the battery reverse polarity state.

Additional features and advantages of the present invention will become more apparent from the following non-limiting examples and by reading the following detailed description of a preferred embodiment of the invention given with reference to the accompanying drawings.

The invention will now be described by way of example with reference to the accompanying drawings.
1 is a schematic diagram of an electrical circuit of a system for controlling an electric motor, in accordance with one embodiment.
2 is a flow diagram of a method for controlling an electric motor system, in accordance with one embodiment.

1 illustrates a non-limiting example of the electronic circuitry of system 100 for control of a direct current (DC) electric motor 112 in a vehicle that preferably utilizes Pulse Width Modulation (PWM) control. The circuit is basically independent from the power source 114 (e.g., a battery), an N-MOS-based switching device (e.g., a contactless relay) 16 in series with the motor 112, (E. G., A microcontroller) to which power is provided. The control device 118 is preferably connected to the N-MOS switching device 116 via terminals 120 and 122. Therefore, the control device 118 sends a control signal to the N-MOS switching device 116 so that the N-MOS switching device 116 switches on the phase of the motor 112 in the battery positive polarity state or the battery reverse polarity state Quot; and "off ".

In order to avoid the disadvantages of the prior art as described hereinabove, the present invention further provides a thyristor 124 connected in parallel with the motor 112. In particular, a silicon controlled rectifier (SCR) type thyristor is a semiconductor device whose direct sense condition can be controlled by application of a current pulse to the gate terminal 126. The conduction is maintained until the current flowing therethrough falls below a certain threshold, referred to as the holding current, in the absence of a signal at the gate terminal 126 once it begins with direct sensing. In the reverse direction, the thyristor 124 normally behaves like a diode, i. E. Does not conduct current.

The thyristor 124 implemented herein has a gate terminal 126 controlled by the control device 118. During normal operation of the system 100 with battery positive polarity, the thyristor 124 operates as a diode and generates a PWM, which can cause the N-MOS switching device 116 to overheat, Thereby preventing a reverse voltage peak inherent to the switching of the motor 112 to be used. To this end, the control device 118 keeps the thyristor 124 always on, i.e., supplying power to its gate terminal 126. Thus, when there is a reverse voltage peak, the thyristor 124 operates as a diode and produces a short circuit at the terminals of the motor 112.

When the circuit is operating with battery reverse polarity, the thyristor 124 is always kept off by the control device 118. That is, the control device 118 stops applying pulses to the gate terminal 126 of the thyristor 124, causing the current to always flow through the motor 112, thereby causing the N-MOS switching device 116 ).

In the particular embodiment shown in Figure 1, the power supply 114 has a nominal voltage of 14.5 volts and the control device 118 is supplied with a voltage of 5 volts. For example, resistors 128 to 138, transistors 140 and 142, capacitors 124 and 142, and so on in order to polarize the voltage of the pulses emitted by the control device 118 to the gate terminal 126 of the thyristor 124. [ A series of elements such as diode 144 and diode 146 may be used, and therefore, in this particular case, the thyristor operates at 14.5 volts. Alternatively, the control device 118 may have the same operating voltage as the thyristor 124, in which case the device would not be needed.

The first resistor 148 and the second resistor 150 are connected to the circuitry to reduce the voltage supplied by the power supply 114. In order to control the voltage applied to the gate terminal 126 of the thyristor 124, . (Current conduction) and "off" state (current nonconductivity) of the thyristor 124 in the battery positive or reverse polarity state, together with the voltage of the pulse generated by the control device 118, The required voltage difference between them is ensured. The first resistor 148 and the second resistor 150 are preferably located between the contact point of one of the poles of the power supply 114 and the gate terminal 126. It is also preferred that the point of contact between the gate terminal 126 of the thyristor 124 and the control device 118 occurs between the first resistor 148 and the second resistor 150.

2 shows a power supply 114, a switching device 116 connected in series with the electric motor 112, a control device 118 for controlling the switching device 116 and a thyristor 124 connected in parallel with the electric motor 112. [ Limiting example of a method 200 for controlling an electric motor system, such as system 100,

The current pulse is applied to the gate terminal 126 of the thyristor 124 and the thyristor is applied to the thyristor 124 when the thyristor is in the positive polarity state. 124).

When the phase of the thyristor is switched to the reverse polarity state of the battery so that the thyristor does not conduct the conduction 212, the thyristor 124 operates as a diode and does not conduct current when the battery is in the reverse polarity state.

Thus, the present invention provides a system 100 and method 200 in which the N-MOS switch 116 is protected under battery reverse polarity and protected against a voltage peak when in battery positive polarity.

While the present invention has been described with reference to preferred embodiments thereof, it is either intended to be limited or not limited solely to the scope of the following claims. In addition, the terms 'first', 'second' and other uses do not denote any order of importance, but rather the terms 'first', 'second', and the like are used to distinguish one element from another Is used. In addition, the terms " day " and others do not denote quantitative limitations, but rather indicate the presence of at least one mentioned item.

Claims (7)

A system (100) for controlling an electric motor (112)
A power source 114;
A switching device 116 connected in series with the electric motor 112 to switch the electric motor 112 between the "on" and "off"
A control device (118) configured to control the switching device (116); And
And a thyristor 124 connected in parallel with the electric motor 112,
The gate terminal 126 of the thyristor 124 is controlled by the control device 118 and thereby controls the current conduction or non-conduction state of the thyristor 124
An electric motor (112) control system (100). The control system (100) of claim 1, wherein the switching device (116) is controlled by the control device (118) using pulse width modulation. The system of claim 1, wherein the switching device (116) comprises an electric motor (112) control system (120) including an N-channel metal oxide semiconductor field effect transistor switching device 100). The control system (100) of claim 1, wherein the control device (118) comprises a microcontroller. The method according to claim 1,
Each of which is connected between one of the poles of the power supply 114 and the point of contact of the gate terminal 126 of the thyristor 124. The first resistor 148 and the second resistor 150 are connected in series, An electric motor (112) control system (100). 6. The method of claim 5,
An electrical motor (112) control system (100) in which the point of contact between the gate terminal (126) of the thyristor (124) and the control device (118) is connected between a first resistor (148) and a second resistor (150). A power supply 114 and a switching device 116 connected in series with the electric motor 112 to switch the electric motor 112 from the "on" state to the "off" state, the control device 118 controlling the switching device 116 , And a thyristor (124) connected in parallel with the electric motor (112), characterized in that the electric motor (112)
The gate terminal 126 of the thyristor 124 is controlled by the control device 118,
Switching the phase of the thyristor (124) to the battery positive state to cause the thyristor (124) to conduct current (210); And
A method (200) for controlling an electric motor (112) system (100) comprising the step of switching an image of a thyristor (124) to a reverse polarity state of the battery so that the thyristor (124) does not conduct current.

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