FR2915640A1 - Solar energy converter for battery charging unit, has control circuit connecting or disconnecting input terminal of hash circuit based on cyclic function ratio of energy variation of image parameter - Google Patents

Abstract

The converter has a voltage adopter (CT) connected between an output terminal (O1) of a hash circuit (CC) and an output terminal (O2) of the converter. A control circuit (CTL) connects or disconnects an input terminal (I1) of the circuit (CC) to the terminal (O1) of the circuit (CC) based on the cyclic function ratio of an energy variation (EC) of an image parameter (VC) that represents the energy stored in an energy storage circuit (C). The variation represents the energy in an energy source (S) and curve of the instant current/voltage charge. An independent claim is also included for a method for controlling a solar energy converter.

Description

The invention relates to a power converter for powering a load

  electrical power from a power source whose available power is subject to significant fluctuations, slow or fast. The invention also relates to a method of controlling such a power converter. The invention can be used with any type of unstabilized energy sources, for example a source composed of photovoltaic cells.

  The energy converter according to the invention can be used in an accumulator charger (commonly known as a battery charger), the electric charge of which is a rechargeable battery, associated or not with a final electrical consumer may consume the energy supplied by the energy source and / or the accumulator. Document FR 2 868 218 in particular discloses a technique for transferring energy between an unstabilized source and an electric charge by pulses of current from a switched capacitor. This technique involves strong currents, which must be tolerated by the electrical load and which are likely to cause electromagnetic disturbances. Also known are DC / DC converters capable of converting the energy of a current source into a constant voltage energy equal to a predefined value. But these converters are generally not adapted to very large fluctuations in the energy supplied by the power source.

  The invention proposes an energy converter, and an associated control method, which does not have the drawbacks of the prior art. Thus, the invention proposes a power converter for supplying an electric charge from a source of energy capable of large fluctuations, said energy converter comprising: a chopping circuit comprising an input terminal capable of to be connected to the power source; - a power storage circuit connected between an output terminal of the hash circuit and a ground; - a voltage adapter connected between the output terminal of the. a chopper circuit and an output terminal of the energy converter that can be connected to the electrical load, said voltage adapter supplying a supply voltage to the electrical load, and - a control circuit adapted to connect or not the input of the hashing circuit at the output of the hashing circuit according to a duty cycle according to the variations of an image parameter representative of an energy stored in the storage circuit, said variations being representative of the energy available in the source and its current load / instantaneous voltage curve.

  According to a particularity, the control circuit is also adapted to regulate the energy consumption of the electric charge according to the image parameter, in particular to regulate the supply voltage, and possibly to stop it, and / or to regulate an impedance of the load electric.

  According to another feature, the image parameter is a voltage present at the terminals of the storage circuit, or the voltage present at the terminals of the high storage circuit squared.

  The present invention also relates to a method of controlling the hash circuit of a converter as defined above comprising a step of varying the duty cycle of the hash control to regulate the variation of the image parameter so as to optimize the acquisition of the energy supplied by the unstabilized source. According to a particular feature, the duty cycle is varied as long as the image parameter is greater than a first value, and the method also comprises a step of: decreasing the supply voltage, when the image parameter is lower than the first value, and / or - to reduce the impedance of the final charge, when the image parameter is less than a second value lower than the first value, and / or to stop the voltage adapter, when the image parameter is less than a third value less than the first value, preferably less than or equal to the second value above, better still less than said second value, and thus, in the case of an electric charge comprising a rechargeable battery and an electrical consumer, let the battery supply the electrical consumer. The present invention also relates to an accumulator charger comprising a power converter as defined above, the output of which is connectable to an electric charge comprising a rechargeable battery, and possibly an electrical consumer whose impedance is susceptible to be regulated by the control circuit. The invention will be better understood and other features and advantages will appear on reading the description which follows, an example of implementation of a power converter according to the invention and a control method. associated. The description is to be read in conjunction with the accompanying drawings in which the single figure is a block diagram of a power converter according to the invention.

  The energy converter CE according to the invention will be described below in the particular context where it is used in a solar battery charger, adapted to supply an electric charge comprising a battery B connected in parallel with an electrical consumer CH final variable impedance, from a source of energy S such as a set of photovoltaic cells, the voltage, current and power of which follow the variations of ambient light energy, highly variable in time.

  From an electrical point of view, the input of the energy converter CE is connected to the variable energy source S. The accumulator B and the electrical consumer CH are connected in parallel between the output 02 of the energy converter CE and the ground and together form the electric load of the energy converter CE.

  The electrical consumer CH is for example a presence detection system, a lighting system, a telephony system, or even several systems possibly having different functionalities and connected in parallel. In the example shown, it is assumed that the impedance of the electrical consumer can be varied by connecting or disconnecting one or more of the systems that constitute it. As stated above, a power converter 10 CE according to the invention comprises: a DC hashing circuit comprising an input terminal Il capable of being connected to the energy source S, a storage circuit of energy C connected between an output terminal 01 of the DC hash circuit and a ground, • a voltage adapter CT, also called a voltage converter, connected between the output terminal 01 of the DC hash circuit and an output terminal 02 of the energy converter capable of being connected to the electrical load, said voltage converter CT supplying a supply voltage VA to the electric load, and a control circuit CTL adapted to connect or not the input It has the DC hashing circuit at the output 01 of the DC hash circuit in a duty cycle function of an image parameter representative of an energy stored in the capacitor C. In one example, the DC hashing circuit 30 simply understand a switch comprising: • an input connected to the input 11 of the hash circuit, a first output connected to the output 01 of the hash circuit and a second output connected to ground, • a control input, connected to the circuit control for receiving a CTLK control signal. When the CTLK signal is active, the switch connects its input to its second output, and when the CTLK signal is inactive, the switch connects its input to its first output. In the example shown in the drawing, the hash circuit CC comprises: an inductance coil L, a first terminal of which is connected to the input 11 of the hash circuit CC, a diode D whose first terminal is connected to a second terminal of the coil L and having a second terminal connected to the output 01 of the DC hash circuit; • a controlled switch K comprising an input connected to the common point of the coil L and the diode D, an output connected to ground and a control input to which a CTLK control signal produced by the control circuit CTL is applied. The diode is said to be free-wheel, it is for example a Schottky diode with a very low forward voltage threshold and a very short switching time, which makes it possible to have a good overall efficiency of the converter.

  When the signal CTLK is active, the switch K is closed, so that the common point of the coil and the diode is connected to the ground: the energy ES supplied by the energy source S accumulates in the L. coil

  Conversely, when the CTLK signal is inactive, the switch K is open, so that the common point of the coil L and the diode D is floating: the energy supplied by the energy source S and the accumulated energy in the coil are transferred to the output 01 of the hash circuit. The CTLK signal is periodic. The period of the CTLK signal (= time between two openings or two closing of the switch K) is of the order of 0.02 to 0.04 milliseconds, ie a hash frequency of 25 to 50 KHz. In the example described, the cyclic ratio a of the signal CTLK is, during a period of the signal CTLK, the time TF during which the switch is closed (which corresponds in the example to an active CTLK signal) divided by the period T of the CTLK signal. The period T is equal to TF + T0, where TO is the time during which the switch K is open (which corresponds in the example to an inactive CTLK signal). a varies between 0 (if the hash circuit is kept open) and 1 (if the hash circuit is kept closed).

  The voltage converter CT is made according to a known scheme, for example a step-down / step-up circuit. From the voltage VC applied to its input, susceptible to fluctuations, it produces a regulated voltage VA on its output 02.

  The energy storage circuit is in the example represented a capacitor C, for example a capacitor of electrochemical type, having a capacity of the order of 1000 to 4700 microFarads. The energy balance of the energy converter according to the invention is as follows: a.ES = EC + EO, with • a cyclic ratio of the control signal CTLK of the hash circuit, • ES, the energy supplied by the source S, • EC, the energy accumulated in the capacitor C, EC = C.VC.VC/2, where VC is the voltage across the capacitor. • EO, the energy consumed by the load downstream of the energy converter, in the example shown, the battery B and the final load CH. The energy storage circuit has a buffering effect between the current source S and the electrical load downstream of the energy converter. When the energy supplied by the current source S is greater than the energy EO consumed by the load, the storage circuit makes it possible to store the energy of the power source that is not consumed by the load and, when the energy provided by the current source S is not sufficient to provide the energy demanded by the electric charge, the storage circuit supplies energy to the load in addition to the energy supplied by the source S.

  The energy accumulated in the storage circuit is equal to EC = C.VC.VC/2. The voltage VC at the terminals of the storage circuit or the product VC.VC are therefore parameters representative of the EC energy available in the storage circuit. If the cyclic ratio a is constant, a variation of the energy EC (and therefore of VC or VC.VC) is representative of a variation of the energy ES supplied by the source (eg: variation of the light power if the source is of the photovoltaic type) or a variation of the energy EO consumed by the electric charge downstream of the energy converter. According to the invention, the control circuit CTL is adapted to connect or not the input 11 of the hashing circuit CC to the output 01 of the hashing circuit CC according to a duty cycle function of an image parameter representative of a stored energy in the storage circuit C. In other words, the control circuit, via the control signal CTLK, controls the opening and closing of the hash circuit and varies the duty cycle a of the signal CTLK as a function of the variations of the image parameter, VC or VC.VC, representative of the variations of the energy stored in the energy storage circuit C. The voltage VC across the circuit C is measured periodically, for example by a digital voltmeter and its value is supplied to the CTL control circuit as input parameter. The VC.VC product is for example calculated circuit product ratio of a means d.e calculation in the control circuit and the desired accuracy for the control of the duty cycle. When the power converter is turned on, the control circuit CTL produces the signal CTLK with a duty cycle a = 0. The duty cycle a is then adjusted to obtain the positive variations between two by means of calculation (not shown) of the order. The choice of the variable VC or VC.VC as an image parameter for controlling the cyclic depends in particular on the presence or absence of 10 periodic measurements of the most important image parameter. In parallel, all the ES energy available in the current source S is transmitted to the load and to the storage circuit C. When ES is greater than E0, the voltage VC increases as the storage circuit stores the energy up to an equilibrium value corresponds to a steady state where ES = E0. If ES is greater than E0, a maximum value VCMAX serves as a stop for the equilibrium value of the image parameter. When the energy stored in the circuit C reaches the storage capacity limit of the circuit C, the voltage VC is at a steady-state value VCMAX and the circuit CTL adjusts the value of the duty cycle a so as to maintain VC at VCMAX. At constant load and energy supplied by the constant source, if a decreases, VC decreases and vice versa. A balance is thus established between the energy supplied by the source S and the energy consumed, while keeping the storage circuit at its maximum load. In a variant, the control circuit is also adapted to regulate, in addition to the duty ratio a, the energy consumption of the load as a function of the image parameter, in the example VC or VC.VC.

  If the load greatly increases its energy consumption, or if the energy supplied by the source drops sharply, then the voltage VC drops and the control circuit CTL adjusts the value of a to obtain the negative variations of the image parameter as small as possible between two periodic measurements until a new equilibrium value. If, despite an optimum value of a (which corresponds to a use of all the ES energy available at the instant considered in the source S), the voltage VC continues to fall, it means that the energy consumed by the electric charge is greater than the energy supplied by the source S and that the storage circuit empties to provide the load with a complementary energy. When VC goes below a first minimum value VCMIN1, lower than VCMAX, it is considered that it is necessary to unload the energy converter, reducing the energy consumption EO of the electric charge. Depending on the electrical load, and the embodiment of the control circuit, the control circuit can, to vary the power consumption of the electric charge according to the value of the image parameter. Regulating the supply voltage VA applied to the electrical load, and / or regulating an impedance of the electrical load, and / or stopping the supply voltage VA applied to the electric load, by stopping the power adapter, CT voltage. For controlling the supply voltage VA, the control circuit may for example produce a control signal CTLVA which is applied to a control input of the voltage adapter CT. The voltage adapter then produces, from the energy it receives from the hash circuit, a VA supply voltage proportional to the level of the CTLVA signal. To control the impedance of the electrical load, the control circuit may for example produce a control signal CTLL which is applied to a control input of the electrical load. The shape and value (s) of the CTLL signal are chosen according to the electrical charge and how its impedance can be varied. In one example, the electrical load comprises an electrical consumer whose impedance can be continuously varied, for example a lamp whose lighting level is continuously adjustable. In this case, the CTLL signal will preferably have a continuously variable level and the electrical consumer impedance will be adjusted according to the level of the CTLL signal (potentiometer). In another example, the electrical load comprises an electrical consumer whose impedance can be varied in stages, for example several electrical devices (control devices, lamps, etc.) connected in parallel and that it is possible to connect or disconnect one by one. In this case, the CTLL signal may for example take several levels, each level indicating the number of devices to be connected or disconnected. The invention also relates to a method for controlling an energy converter as described above. Naturally, the process must be adapted to the chosen embodiment of the energy converter. In practice, the method is implemented by the control circuit CTL. The method according to the invention comprises a step of: • varying the duty cycle a to regulate the image parameter around a steady state value (VCMAX) synonymous with the best adaptation in terms of impedance of the converter to the curve of charge 5 current / voltage of the source S. In other words, the duty cycle is adjusted so that, in steady state, the electric charge receives the energy EO it needs and the storage circuit remains charged. The duty cycle is varied as long as the image parameter is greater than a first VCMIN value. Alternatively, the method may further comprise a step of: • when the VC image parameter is less than the first VCMIN1 value, decreasing the VA supply voltage supplied to the load. If the image parameter falls below the first value VCMIN1, it means that the EO energy consumed by the load is greater than the ES power supplied by the source. Decreasing the supply voltage then reduces the energy consumed by the load. This variant is for example advantageous if the load comprises a rechargeable battery: when charging the accumulator, the current consumed by the accumulator is a function of the voltage which supplies it. In another variant, when used for a converter supplying an electric charge comprising an electrical variable impedance consumer, the method may further comprise a step consisting of: when the image parameter is less than a second lower value VCMIN2 at the first value VCMIN1, decrease the impedance of the energy consumer.

  If the VC image parameter falls below the second value VCMIN2, it means that, despite the lowering of the supply voltage, the energy consumed by the load remains greater than the energy supplied by the source. In this case, reducing the impedance of the electrical consumer reduces the energy it consumes. If this is not enough because the ES energy supplied by the source is too low, and in particular if the VC image parameter falls below a third value VCMIN3 lower than the second value VCMIN2, the control circuit CTL decides to stopping the CT voltage adapter using the CTLVA signal to let the DC hash circuit reload capacitor C at a duty cycle to ensure the largest positive image parameter variations between two periodic measurements. Once this image parameter has reached its maximum value, the CT adapter is restarted. During this mode, it is the battery that powers the load.

Claims (10)

  An energy converter for supplying an electric charge (B, CH) from a power source (S) capable of large fluctuations, said energy converter comprising: a chopping circuit (CC) comprising an input terminal (11) which can be connected to the power source (S), an energy storage circuit (C) connected between an output terminal (01) of the hash circuit (CC) ) and a ground, • a voltage adapter (CT) connected between the output terminal (01) of the hash circuit (CC) and an output terminal (02) of the energy converter that can be connected to the load electrical, the so-called voltage adapter (CT) providing a supply voltage (VS) to the electrical load, and • a control circuit (CTL) adapted to connect or not the input (II) of the hashing circuit ( CC) at the output (01) of the hash circuit (CC) in a cyclic ratio according to the variations of an image parameter (VC, VC.VC) representative of an energy stored in the storage circuit (C), said variations being representative of the available energy in the source (S) and of its current / instantaneous voltage charge curve).   2. Converter according to claim 1, wherein the control circuit is also adapted to regulate the energy consumption of the electric charge according to the image parameter.   The converter according to claim 2, wherein the control circuit is adapted to regulate: the supply voltage, and / or an impedance of the electrical load.   4. Converter according to one of the preceding claims, wherein the image parameter is: a voltage (VC) present at the terminals of the storage circuit (C), the voltage present at the terminals of the storage circuit (C) elevated squared.   5. A chopping circuit control method of a converter according to one of the preceding claims, comprising a step of: • varying the duty ratio (a) to regulate the variation of the image parameter, so as to optimize the acquisition of the energy supplied by the unstabilized source.   The method of claim 5, wherein the duty cycle is varied as long as the image parameter is greater than a first value (VCMIN), and also comprising a step of: when the image parameter (VC) is less than the first value (VCMIN1), decrease the supply voltage (VA). 25   7. Method according to one of claims 5 or 6 taken in combination with claim 3 or claim 4, also comprising a step of. • when the image parameter (VC) is less than 30 a second value (VCMIN2) lower than the first value (VCMIN1), reduce the impedance of the final load.   The method according to one of claims 5 to 7, taken in combination with claim 3 or claim 4, further comprising a step of: when the image parameter (VC) is less than a third value (VCMIN3) lower at the first value (VCMIN1), stop the voltage adapter (CT).   9. Battery charger comprising a power converter according to one of claims 1 to 4, the output of which is connectable to an electric charge comprising a rechargeable battery.   10. Charger according to claim 9 taken in combination with one of claims 3 to 4, the output of which is connectable to an electrical load comprising a rechargeable battery and an electrical consumer whose impedance is likely to be regulated by the control circuit.