Contactless power supply system

Abstract

The secondary voltage is controlled without the need for special communication methods. [Solution] A primary side power supply signal of a first frequency is supplied to the primary side coil 20-1, and a detection voltage signal of a second frequency corresponding to the output voltage is supplied from the secondary side coil 20-2 to the secondary side coil 20-2. The primary side detection voltage signal generated in the primary side coil 20-1 is extracted and the amplitude of the primary side power supply signal is controlled based on this.

Description

Technical Field

[0006] , , , ,

[0001] The present disclosure relates to a contactless power supply system having a primary coil and a secondary coil.

Background Art

[0002] In a conventional contactless power supply system, power is supplied from the primary coil of a transformer to the secondary coil. Therefore, depending on the coil specifications of the transformer, the output voltage obtained by rectifying the secondary voltage is adjusted to a desired voltage. In addition, in order to more accurately control the output voltage, it has also been proposed to detect the state of the output voltage and control the drive of the primary coil (see Patent Document 1). In Patent Document 1, the detected voltage on the secondary side is supplied to the primary circuit by optical communication using a photocoupler.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in order to communicate and transmit information between the primary circuit and the secondary circuit, a circuit for that purpose is required. In addition, optical communication cannot be used in an environment where light is blocked.

[0005] For example, when using a contactless power supply system in an electric vehicle (BEV) or a hybrid electric vehicle (HEV), it may be necessary to reduce the size or to communicate within oil. <N

Means for Solving the Problems

[0006] The contactless power supply system according to this disclosure includes: a primary side power supply signal generating unit that generates a primary side power supply signal of a first frequency; a primary side coil to which the primary side power supply signal is supplied; a secondary side coil that is magnetically coupled to the primary side coil and generates a secondary side power supply signal corresponding to the primary side power supply signal supplied to the primary side coil; a rectifier that rectifies and outputs the secondary side power supply signal; a secondary side detection voltage signal generating unit that generates a detection voltage signal of a second frequency different from the first frequency, corresponding to the output voltage of the rectifier; a secondary side drive unit that supplies the secondary side detection voltage signal to the secondary side coil; an extraction unit that separates and extracts the primary side detection voltage signal generated in the primary side coil in response to the secondary side detection voltage signal from the primary side power supply signal; and an amplitude control unit that controls the amplitude of the primary side power supply signal based on the extracted primary side detection voltage signal. [Effects of the Invention]

[0007] This eliminates the need for special transmitting and receiving means for signal transmission from the secondary side to the primary side, allowing for a smaller device and enabling use even in environments where light is blocked. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram showing the configuration of a contactless power supply system according to an embodiment. [Figure 2] This section describes the comparison of signal waveforms using a comparator. [Figure 3] This figure shows the relationship between the distance between the primary and secondary coils and the output voltage of the rectifier in the contactless power supply system of this embodiment. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are not limiting to this disclosure, and configurations formed by selectively combining multiple examples are also included in this disclosure.

[0010] Figure 1 shows the configuration of a contactless power supply system according to an embodiment.

[0011] It has a primary circuit and a secondary circuit that are physically separated. Power generated in the primary circuit is transmitted to the secondary circuit without contact, and the transmitted power is used to drive the load in the secondary circuit.

[0012] The AC oscillator 10 generates an AC signal of a first frequency. The AC signal is supplied to the analog multiplier 12, where it is multiplied by a coefficient Vfb and supplied to the amplifier 14 as an AC signal of a predetermined amplitude. The analog multiplier 12 functions as an amplitude control unit.

[0013] The pair of outputs of amplifier 14 are connected to both ends of the primary coil 20-1. Amplifier 14 supplies a primary power supply signal corresponding to the AC signal input from analog multiplier 12 to the primary coil 20-1. A pair of capacitors 16a and 16b are placed between amplifier 14 and primary coil 20-1 to cut the DC component. The output voltage (AC voltage) of amplifier 14 is denoted as V1. The section from AC oscillator 10 to amplifier 14 functions as the primary power supply signal generation section.

[0014] An alternating current (referred to as the secondary power supply signal) corresponding to the alternating current flowing through the primary coil 20-1 flows through the secondary coil 20-2. The primary coil 20-1 and the secondary coil 20-2 are magnetically coupled and function as a transformer 20 that transmits signals between the two coils without contact.

[0015] A rectifier 22 is connected to the secondary coil 20-2. The rectifier 22 rectifies the secondary power supply signal input from the secondary coil 20-2 and outputs the corresponding DC power. In this example, one output of the rectifier 22 is connected to ground, and the other output outputs a DC voltage corresponding to the amplitude of the secondary power supply signal input. This DC voltage is regulated by the regulator 24 to a predetermined output voltage, for example, 3.3V, and supplied to the load 30. In this way, the load 30, which is far from the primary circuit, can be driven at a predetermined voltage. It is preferable for the regulator 24 to obtain an output voltage lower than the input voltage; for example, the output voltage V2 of the rectifier 22 is set to about 7V to obtain an output of 3.3V.

[0016] Here, the voltages across the regulator 24 are supplied to the voltage / pulse density converter 32. The voltage / pulse density converter 32 is supplied with a second-frequency pulse signal from the oscillator 34. The voltage / pulse density converter 32 converts the voltages across the regulator 24 into pulse signals with a pulse density corresponding to the voltage difference across the regulator 24. For example, the larger the voltage difference, the higher the pulse density of the pulse signal, but the opposite is also acceptable. The reference pulse density is preferably set to correspond to the target value of the voltage difference across the regulator 24, and can be appropriately determined to facilitate overall operation such as transmission to the primary side. The voltage / pulse density converter 32 functions as a secondary-side detection voltage signal generator.

[0017] The pair of outputs of amplifier 36 are connected to both ends of the secondary coil 20-2. A pulse signal is supplied to the secondary coil 20-2 via amplifier 36. This is superimposed on the secondary power supply signal of the secondary coil 20-2. Therefore, amplifier 36 functions as a secondary drive unit. The signal supplied to the secondary coil 20-2 is also called the secondary detection voltage signal.

[0018] In the path between the amplifier 36 and the secondary coil 20-2, a switch 38 and a pair of capacitors 40a and 40b are arranged. When the switch 38 is turned off, the voltage / pulse density converter 32 is disconnected from the secondary coil 20-2. The capacitors 40a and 40b are for blocking the low-frequency secondary power supply signal from flowing to the amplifier 36 side and supplying the pulse signal to the secondary coil 20-2.

[0019] The input voltage and the output voltage of the rectifier 22 are supplied to the comparator 42. The comparator 42 determines whether the secondary circuit connected to the secondary coil 20-2 has a low impedance below a predetermined value from the comparison of the input signals. When the secondary side of the transformer 20 has a predetermined low impedance, the switch 38 is turned off. This prevents devices such as the voltage / pulse density converter 32 from being damaged by the secondary power supply signal.

[0020] A differential single converter 50 is connected to both ends of the primary coil 20-1. The differential single converter 50 converts the signal to a signal of a predetermined voltage (for example, 0V) or higher. The output of the differential single converter 50 is supplied to a high-pass filter (HPF) 52, where only the high-frequency signal is passed through. The pulse signal sent from the secondary side is high-frequency, and the pulse signal is extracted. Regarding the pulse signal from the high-pass filter 52, the waveform shaping unit 44 shapes the waveform so that the area of each pulse is the same, and then supplies it to the low-pass filter 46. The low-pass filter 56 outputs a voltage signal corresponding to the density of the pulse signal. Note that the differential single converter 50 and the high-pass filter 52 constitute an extraction unit.

[0021] Therefore, this signal (referred to as the primary side detection voltage signal) indicates the difference between the input and output of the regulator 24 of the secondary circuit, that is, the difference between the voltage supplied to the load 30 and the output of the rectifier 22. The target is to make the output voltage of the rectifier 22 coincide with the input target voltage of the regulator 24, and it has a voltage value corresponding to the error from the target value of the amplitude of the drive signal of the primary coil 20-1.

[0022] The output of the low-pass filter 56 is supplied to the sample-and-hold circuit (S / H) 58. The sample-and-hold circuit 58 is supplied with an S / H signal from the comparator 60.

[0023] The comparator 60 is supplied with the output of the AC oscillator 10 and a predetermined threshold value VTH1, and an S / H signal is generated from the comparison results of these.

[0024] Here, the comparison of signals in the comparator 60 is shown in FIG. 2. Thus, the AC signal that is the output of the AC oscillator 10 is a sine wave of the set frequency. The threshold value VTH1 is a signal indicating the set amplitude of the AC signal. Then, by comparing the two, a pulse indicating a predetermined range around the position of the amplitude center (for example, V) of the AC signal is obtained, and this becomes the S / H signal.

[0025] The sample-and-hold circuit 58 samples the voltage signal from the low-pass filter 56 near 0V of the AC signal when the S / H signal is at the H level, and supplies the sampled signal to the error integrator 62. As a result, the output of the low-pass filter 56 corresponding to the pulse signal extracted near 0V of the power supply drive signal flowing through the primary coil 20-1 is adopted.

[0026] In addition to the signal from the sample-and-hold circuit 58, the error integrator 62 is supplied with a threshold value VTH2, and integrates the difference between the two with a predetermined time constant. The threshold value VTH2 is the expected value of the value of the signal supplied from the sample-and-hold circuit 58, and the error integrator 62 integrates the difference from the expected value and supplies the obtained value to the analog multiplier 12 as the coefficient Vfb.

[0027] Here, the target is that the input / output difference of the normal regulator 24 is a predetermined positive value, and in that case, the output value of the sample-and-hold circuit 58 when the output pulse of the voltage / pulse density converter 32 is transmitted to the primary side corresponds to the threshold value VTH2. Note that the threshold value VTH2 can be set to an appropriate value in consideration of losses in the signal transmission path and the like.

[0028] In this way, a feedback loop is formed based on controlling the coefficients of the analog multiplier 12 so that the voltage V2, which is the output of the rectifier 22, matches the output of the regulator 24. The integral time constant in the error integrator 62 should be set to an appropriate value considering the stability of the feedback loop.

[0029] Furthermore, in order to enable constant bidirectional communication using transformer 20, the frequency bands for driving the primary coil 20-1 and the frequency bands for driving the secondary coil 20-2 are separated. For example, the primary drive frequency is set to approximately 100 kHz, and the secondary drive frequency to approximately 1 MHz. In the primary circuit, the primary coil 20-1 is driven via a circuit that has low impedance around 100 kHz and high impedance around 1 MHz. In the secondary circuit, the secondary coil 20-2 is driven via a circuit that has low impedance around 1 MHz and high impedance around 100 kHz. This frequency separation ensures reliable bidirectional communication.

[0030] Figure 3 shows the relationship between the distance between the primary coil 20-1 and the secondary coil 20-2 and the output voltage V2 of the rectifier 22 in the contactless power supply system of this embodiment. As shown, a stable output voltage V2 can be obtained even with a relatively wide coil distance. In the illustrated example, the output voltage is 7V when the distance between the coils is almost 0mm, and the output voltage V2 is 6.5V even with a distance between the coils of 5mm, demonstrating that the desired output voltage V2 can be obtained with a wide distance between the coils.

[0031] Thus, according to the contactless power supply system of this embodiment, communication between the secondary circuit and the primary circuit can be performed using the transformer 20. Therefore, there is no need to provide separate communication means such as a photocoupler, and the entire system can be miniaturized. Furthermore, since optical communication is not used, communication is possible even when the system is submerged in oil where light is blocked.

[0032] The ample distance between coils allows for power supply without overvoltage or undervoltage, thus improving the flexibility of instrumentation. [Explanation of Symbols]

[0033] 10 AC oscillator, 12 analog multiplier, 14 amplifier, 20 transformer, 20-1: primary coil, 20-2: secondary coil, 22 rectifier, 24 regulator, 30 load, 32 pulse density converter, 34 oscillator, 36 amplifier, 38 switch, 42 comparator, 44 waveform shaping section, 46 low-pass filter, 50 differential single-ended converter, 52 high-pass filter, 56 low-pass filter, 58 sample-and-hold circuit, 60 comparator, 62 error integrator.

Claims

[Claim 1] A contactless power supply system, A primary side power supply signal generator that generates a primary side power supply signal of a first frequency, The primary coil to which the primary power supply signal is supplied, A secondary coil that is magnetically coupled to the primary coil and generates a secondary power supply signal corresponding to the primary power supply signal supplied to the primary coil, A rectifier that rectifies and outputs the secondary power supply signal, A secondary side detection voltage signal generating unit generates a detection voltage signal of a second frequency different from the first frequency, corresponding to the output voltage of the rectifier. A secondary drive unit that supplies the secondary detection voltage signal to the secondary coil, An extraction unit that separates and extracts the primary side detection voltage signal generated in the primary side coil in response to the secondary side detection voltage signal from the primary side power supply signal, An amplitude control unit controls the amplitude of the primary side power supply signal based on the extracted primary side detection voltage signal, including, Contactless power supply system.

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