CN1913334A - Speed regulating fan system with fault-tolerant capacity - Google Patents

Abstract

This invention relates to a fan regulation system with an error-tolerance ability including an input voltage testing circuit, a PWM circuit, a switch supply circuit and a fan set, in which, the control signal of rotation speed of the system and tested voltage signal control the output of the PWM waveforms, control the switch devices of a switch supply circuit and output a suitable voltage to the fan set, when the fan is tested to be faulty, the duty ratio of the PWm waveform can be adjusted.

Description

Fault-tolerant adjustable-speed fan system

technical field

The invention relates to a fan system for air cooling and heat dissipation of communication and large computers, in particular to a fan cooling device for communication equipment.

Background technique

In the fields of communications and large-scale computers, with the development of technology, the power consumption of equipment tends to increase gradually, which puts forward higher requirements for the heat dissipation performance and reliability of the heat dissipation system. At present, the main heat dissipation method in this field is to use cooling fans for active air cooling. In order to obtain better heat dissipation effects, the power of cooling fans also tends to increase, which leads to increased power consumption and noise of the fan system.

In the traditional fan system, the fan is powered directly by the -48V power supply of the communication system. Under the current technical conditions, some problems are gradually exposed, including:

1. The power supply voltage of the fan varies with the power supply voltage of the rack, which may cause poor heat dissipation when the power supply voltage is low, and excessive power consumption and extra noise when the voltage is high;

2. The speed of the fan is not controlled, which may cause poor heat dissipation when the ambient temperature is high, and generate additional power consumption and noise when the ambient temperature is low;

3. The fan itself contains a mechanical structure, and its service life is much shorter than that of semiconductor devices. The fault tolerance of the fan failure should be considered in the design of the fan system. Although fault tolerance can be achieved directly by adding additional fans, when all fans are running normally, additional power consumption and noise are generated;

In order to solve these problems, there are some improved fan control methods, which bring some disadvantages while improving the traditional fan system. Common methods such as:

1. Use a linear regulated power supply to supply power to the fan, but this can only control the speed and reduce noise, but cannot significantly reduce power consumption; and the power consumption of the voltage conversion device is too large, resulting in reduced reliability;

2. Using a special speed-regulating fan, an additional control signal can be used to control the fan speed. The fan uses a special design (non-switching power supply mode) inside, the price is relatively expensive, and only a few suppliers produce it, so there is a supply risk;

3. Use a separate switching power supply to generate a lower half-speed voltage, and the power supply of the fan can be switched between the input power supply voltage and the half-speed voltage, but such a control method cannot realize the continuous change of the fan speed and reduce the power The effects of loss and noise are limited;

4. Use a switching power supply with continuously adjustable output voltage and voltage regulation through feedback to supply power to the fan. For a switching power supply whose output voltage can be adjusted in a wide range, it is difficult to design and debug, and the cost is high to ensure stable operation under various output voltages and load conditions. Not only the long debugging cycle will affect the development progress, even if it can be realized, it will inevitably reduce the reliability due to the influence of the feedback circuit.

5. By detecting the status signal of each fan, it is judged whether the fan is faulty, and then the speed of the fan group is adjusted to achieve fault tolerance. But when the fan fails and the status signal does not give an indication (it also fails), it will cause poor cooling of the system, which may lead to serious consequences;

6. By detecting the current consumed by each fan to determine whether the fan is faulty, and then adjust the speed of the fan group to achieve fault tolerance. Although it is more reliable to detect fan faults in this way, when the fan speed is required to be continuously adjustable, the fan current will change continuously, and a more accurate detection of the fan current is required to determine whether it is faulty, which increases the cost.

Contents of the invention

The purpose of the present invention is to provide a speed-regulating fan system with fault tolerance, which can overcome the defects of the prior art, and use ordinary fans according to the control signal of the system to realize intelligent speed adjustment and significantly reduce the power consumption of the cooling system and noise; it can adapt to different ambient temperatures and power supply voltages, and make stable control of the fan voltage.

The invention includes an input voltage detection circuit, a PWM (Pulse Width Modulation, pulse width modulation) control circuit, a switching power supply circuit and a fan group; the PWM control circuit controls the output PWM waveform by the speed control signal of the system and the detected voltage signal, and controls the switch The switching device of the power circuit outputs an appropriate voltage to supply power to the fan group. And when a fan failure is detected, certain adjustments can be made to the duty cycle of the PWM waveform.

Described input voltage detection circuit can be made of 1 or more special voltage detection chips (such as the MC34161 voltage detection chip of ONSEMI); It can also be made of general voltage comparator or operational amplifier (such as LM324); It can be composed of A/D converter or VFC circuit; convert the voltage signal into level, period, frequency, duty cycle or some kind of data frame signal.

The fan speed control signal may be provided by an environment monitoring unit of the communication system.

The PWM control circuit is realized by a programmable logic device or a single chip microcomputer.

Compared with the prior art, since the present invention uses an open-loop switching power supply controlled by a logic circuit to supply power to the fan, the following improvements have been achieved:

Through the continuous adjustment of the fan voltage, the speed can be continuously adjusted by using an ordinary fan, which significantly reduces the power consumption and noise of the cooling system; the high-efficiency switching power supply is used, and there is no common stability problem on the switching power supply, improving The reliability is improved; while the fault tolerance is realized, there is no extra noise and power consumption on the fan.

Description of drawings:

Fig. 1 is a general block diagram of the present invention;

Figure 2 is the V-I characteristic curve of the BUCK circuit under the control of the PWM waveform with a fixed duty ratio;

Figure 3 is an example of a power supply voltage detection circuit (VFC circuit realized by LM331);

Figure 4 is a schematic diagram of a BUCK converter with negative voltage input commonly used in communications;

Fig. 5 is a functional block diagram of a PWM control circuit realized by a programmable logic device.

Detailed ways:

The implementation of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Figure 1 is the overall block diagram of the system. The whole system is composed of input voltage detection circuit, PWM control circuit, switching power supply circuit and fan group. The PWM waveform output by the PWM control circuit is controlled by the speed control signal of the system and the detected voltage signal. This waveform controls the switching device of the switching power supply and outputs an appropriate voltage to supply power to the fan group. And when a fan failure is detected, certain adjustments can be made to the duty cycle of the PWM waveform.

The input voltage detection circuit can be composed of one or more specialized voltage detection chips, such as ONSEMI's MC34161 voltage detection chip; it can also be composed of a general-purpose voltage comparator or operational amplifier, such as LM324; it can also be converted by A/D device or VFC circuit. Its purpose is to convert the voltage of the input power supply into a signal that can be recognized by the PWM control circuit (digital circuit). The signal can be level, period, frequency, duty cycle, or even some kind of data frame.

Figure 3 is an example of a voltage detection circuit. It is a typical VFC (Voltage-Freqence Convter, voltage-frequency converter) circuit composed of LM331, which can convert a voltage signal into a frequency signal and maintain a linear relationship between voltage and frequency. In the figure, V _IN is the input voltage, V _S is the power supply of LM331, V _LOGIC is the pull-up power supply for the output frequency signal, and f _OUT is the frequency output. In order to make the input voltage range conform to the input range of the VFC circuit, a resistor can be used to divide the voltage first, and then the voltage-frequency conversion can be performed.

The rotational speed control signal in FIG. 1 can be provided by the environmental monitoring unit of the communication system. The environmental monitoring board of the communication system contains a CPU and some sensors. The software it runs can output a signal to control the fan speed to the PWM control circuit according to the input conditions such as the current operating temperature and the power of the system. The signal can also be level, period, frequency, duty cycle, or even some kind of data frame.

The PWM control circuit can be conveniently implemented with a programmable logic device, as shown in Figure 5; there are also other implementation methods, such as a single-chip microcomputer. It is required to calculate a specific duty ratio D according to the received power supply voltage signal and the speed control signal given by the environmental monitoring board, and output the corresponding PWM waveform to control the switching power supply to obtain the required voltage. And the duty cycle of PWM can be adjusted according to the status signal of the fan.

The switching power supply circuit can be a common open-loop BUCK converter. Figure 4 is an example of a BUCK converter, which mainly includes power switching tubes, freewheeling diodes, inductors, and input and output capacitors. Its input voltage V is negative, the output voltage V_FAN is also negative, and GND is the common ground of the input and output voltages. The PWM signal output by the PWM control circuit is driven to generate the switch control signal MOS_G of the MOS device in the figure to control the on-off of the device. In order to obtain good impedance-frequency characteristics, the output capacitor is used in parallel with an electrolytic capacitor and a ceramic capacitor.

A fan group contains multiple fans. Each fan includes a working state indication signal, generally a level signal used to indicate a fault or a frequency signal indicated a rotating speed. These status signals are all output to the PWM control circuit.

In order to describe the working principle of the present invention, first define the circuit parameters of the BUCK power converter as follows:

T switching period;

T _ON switch conduction time

D The duty cycle of the switch, that is, T _ON /T

I output average current

V _IN input voltage

V _OUT output voltage

L inductance value

According to the theory of switching power supply, the BUCK converter has two working states, which are current continuous working mode and current discontinuous working mode, and its critical point is

T*(1-D)* _VOUT ＝2*I*L (1)

When the current is greater than this critical point, the power supply is in the current continuous working mode, and its output voltage is:

V _OUT =V _IN *D (2)

When the current is less than this critical point, the power supply is in the current discontinuous working mode, and its output voltage is:

V _OUT ＝T _ON ² *V _IN ² /(2*I*T*L+T _ON ² *V _IN ) (3)

According to (1), (2) and (3), the output characteristic curve of the BUCK converter at a fixed duty ratio can be obtained, as shown in Figure 2, where the abscissa represents the current and the ordinate represents the voltage.

According to the formula (1), the inductance value L of the BUCK converter and the period T of the output waveform of the PWM control circuit are designed, so that the working current of the power supply is just greater than the critical point of continuous/discontinuous current when the fan group is not faulty. At this time, the output voltage of the power supply is determined by formula (2). According to formula (2), we can get:

D＝V _OUT /V _IN (4)

Wherein, V _IN is given by the voltage detection circuit, and V _OUT is determined by the fan speed control signal output from the environment monitoring unit of the system to the PWM control circuit. The PWM control circuit is based on formula (4) as the basis for outputting the duty cycle D of the PWM signal.

Referring to Fig. 5, the PWM control logic is composed of voltage signal receiving logic, rotational speed signal receiving logic, duty cycle calculation logic and PWM generation logic. The voltage signal receiving logic and the speed signal receiving logic are used to receive the voltage and speed control signals (frequency, duty cycle, etc.), and convert them into a corresponding value inside the logic. The duty cycle calculation logic is based on formula (4 ) to calculate the corresponding duty cycle D. Because the numerical calculation inside the logic is too complicated, it is realized by look-up table. The PWM generation circuit outputs a corresponding PWM waveform according to the duty cycle D.

It is easy to see that when the input voltage V _IN changes, it will lead to a change in the measured voltage signal. After receiving this change, the PWM control circuit will adjust the value of D according to formula (4) to ensure the V _OUT power supply for the fan. basically stable. Similarly, when the fan speed control signal output by the system environment monitoring unit changes, the duty cycle D will also change accordingly, and V _OUT is adjusted to achieve the purpose of controlling the speed. After obtaining the duty ratio D, the output of the PWM waveform is relatively simple.

Because the switching power supply works in an open-loop state, there is no output voltage feedback, so there will never be stability problems such as self-excitation of the power supply. Compared with the circuit with feedback, although the stability of the output voltage will drop slightly (caused by factors such as the resistance on the wire), but because the fan has relatively low requirements for the stability of the power supply voltage, this shortcoming can be completely ignored.

Because the working current of the fan group under normal conditions is just greater than the critical point of continuous/discontinuous current, when individual fans fail and the current of the fan group decreases, it will cause the power supply to enter the current discontinuous working state. At this point, the output voltage of the power supply is determined by formula (3). Referring to Figure 2, it can be seen that as the load current decreases, the circuit will gradually enter a current discontinuous working state, and the output voltage will increase. The speed of other fans will be increased to make up for the loss of ventilation volume of the faulty fan and maintain the overall ventilation volume of the system basically stable.

This adjustment process is automatically completed by the switching power supply and has nothing to do with the PWM control circuit. Even if the faulty fan does not give an abnormal status signal, the fault tolerance mechanism is still effective.

When a fan in the system is faulty, its fault status may be reflected in the status signal. The status signals of the fan are all output to the PWM control circuit, which can detect the failure of the fan (abnormal status signal level or frequency). In addition to sending out the alarm signal of the fan according to the fault information of the fan, the PWM control circuit can also adjust the duty cycle D of the output PWM signal according to a certain algorithm to increase the speed of the non-faulty fan and compensate for the loss of ventilation of the faulty fan , to achieve the purpose of fault tolerance.

The algorithm for adjusting the duty ratio D is based on the principle of maintaining the power of the fan group basically stable. Generally, the load characteristic of the fan is very close to the resistance. For example, in a system with N fans, when one fan is damaged, according to the principle of maintaining the power of the fan group basically stable:

N*V ² =(N-1)*V ₁ ² (5)

Easy to get:

V ₁ =(N/(N-1)) ^1/2 *V (6)

In formula (5) and formula (6), V represents the output voltage of the power supply when all the fans are normal, and V ₁ represents the output voltage of the power supply when a fan fails.

Claims (5)

1, a kind of speed regulating fan system that fault-tolerant ability is arranged comprises input voltage detection circuit, pulse width modulation control circuit, switching power circuit and fan group;

Described input voltage detection circuit is realized the measurement to input supply voltage, and converts the voltage signal that measures to signal that pulse width modulation control circuit can be discerned;

The rotation speed of the fan control signal that described pulse width modulation control circuit provides according to the signal and the system of detected voltage detecting circuit output is calculated and to the pulse width modulated waveform of a scalable duty ratio of switching power circuit output; Accept the status signal that fan is sent, the pulse-width modulated waveform is made certain adjustment;

Described switching power circuit utilizes the pulse width modulated waveform control of pulse width modulation control circuit output, exports an adjustable voltage and supplies with fan, realizes speed governing; Fan hinder for some reason cause power to reduce after, enter the discontinuous operating state of electric current, improve output voltage automatically.

2, the described speed regulating fan system that fault-tolerant ability is arranged of claim 1, it is characterized in that, described input voltage detection circuit, be to constitute, convert voltage signal to level, cycle, frequency, duty ratio or certain data frame signal by at least 1 special voltage checking chip, general voltage comparator or operational amplifier, A/D converter or voltage-freq converting circuit.

3, the described speed regulating fan system that fault-tolerant ability is arranged of claim 1 is characterized in that the rotation speed of the fan control signal is provided by the Environment Monitor Unit of communication system.

4, the described speed regulating fan system that fault-tolerant ability is arranged of claim 1 is characterized in that, chip microcontroller is realized or used to described pulse width modulation control circuit with programmable logic device.

5, the described speed regulating fan system that fault-tolerant ability is arranged of claim 4, it is characterized in that, described programmable logic device realizes that pulse width modulation control circuit comprises the voltage signal receive logic, tach signal receive logic, duty ratio computational logic and pulse width modulation formation logic; Voltage signal receive logic and tach signal receive logic are used for receiving voltage and speed controling signal, and convert it to a value corresponding of logic inside, calculate corresponding duty ratio by the duty ratio computational logic.

Images