Control system of bidirectional power converter

Abstract

The invention discloses a control system for a bidirectional power converter. The control system comprises a control circuit for controlling a bidirectional DC-DC converter, a circuit for providing an auxiliary power supply voltage for one or more amplitude limiting operational amplifiers, and a circuit for generating a regulation reference voltage for forward or reverse current limitation in the control circuit. The control system is particularly suitable for a bidirectional programmable power supply, and has the functions of voltage regulation, bidirectional precise adjustable current limitation, bidirectional precise adjustable power limitation, parallel precise adjustable constant resistance control, reverse control and forward series constant resistance control. When a load condition or a program mode value changes, the control system allows control to rapidly shift from one mode to another, and allows the converter output current direction to change seamlessly, and eliminates the tendency of the control circuit to oscillate at the boundaries of the various control modes. According to the invention, the control dead zone of current limitation or power limitation can be reduced or eliminated to the greatest extent when the output current is extremely low.

Description

Technical Field

[0001] The present invention relates to the technical field of high-frequency switching power supply converters, including AC-DC, DC-DC or DC-AC power electronic converters, and in particular to an AC-DC switching mode programmable power supply. Background Art

[0002] Programmable Power Supplies (PPS) were originally called laboratory power supplies and feature a precise, adjustable voltage output and current limit programmed via a front panel potentiometer. Until the introduction of the Anatech Electronics Lab 3000 series in 1980, these power supplies were inefficient linear regulators. Switch-mode types, such as the Lab 3000 series, are now becoming more popular due to their high efficiency and compact size. In recent years, there has been an increasing demand for bidirectional switch-mode programmable power supplies that can both source (forward) and sink (reverse) load current, due to the advent of battery electric vehicles and the need to test batteries, inverters, converters and chargers. There is an increasing need for a wide range of precisely programmable output voltages, precise and adjustable current limit and power limit in both directions of these bidirectional programmable power supplies. Precise and adjustable shunt constant resistance control in the reverse direction and series constant resistance control in the forward direction are also often required. These different control modes should exist simultaneously, but ideally only one mode should be regulating the load current at any time. Furthermore, it is desirable that the control mode be able to change seamlessly from one mode to another with minimal delay time and without oscillation at the boundaries of the control modes. Traditionally, control systems for these laboratory or programmable power supplies have used analog circuits using operational amplifiers (Operational Amplifiers) or dedicated pulse width modulation (PWM) control ICs, however, delay issues in transferring control modes and oscillations have plagued such analog controls. Recently, digital control systems have been proposed because they are more flexible and less prone to oscillations. However, digital control is inherently slower than analog control because there are inevitable time delays in sensing voltage and current sampling and calculation delays, further slowing down the response speed.

[0003] The SG1524 from Silicon General (now manufactured by Microchip) is one of the earliest dedicated pulse width modulation (PWM) control ICs designed specifically for controlling switch-mode power converters. Figure 2 The voltage error op amp is a transconductance op amp. The current error op amp is a low bandwidth, low gain differential op amp with an input offset voltage of 200mV. Therefore, the transition to current limit mode is slow and imprecise. A later dedicated PWM control IC is the TL494 from Texas Instruments (TI), whose schematic is shown in Figure 3 together and pulled down by a 0.7mA constant current sink. This allows selection of either constant voltage mode or constant current mode. This configuration produces more precise control and fast transitions between voltage control mode and current limit mode, but may result in oscillations at the crossover point between the two modes as one control loop is loaded by the compensation network of the other control loop.

[0004] The control method used by TL494 can be extended to more modes, such as power limiting or constant resistance limiting, but the crossover oscillation problem will be more serious, and the method cannot be extended to bidirectional control.

[0005] Recently, two digital control methods have been proposed to realize multi-loop control of bidirectional converters. Figure 4 As shown, a main voltage control loop is involved, in which the measured output voltage Vs is subtracted from the desired voltage setting input Vset to establish a voltage error value, which is amplified by the transfer function Gv and then input to the pulse width modulator Kpwm. Various other control loops (such as the positive current loop) function to reduce the voltage setting input Vset of the voltage loop to limit the load current in the positive or negative direction. Therefore, at least two of these loops, namely the voltage loop and one of the current or power limiting loops, act simultaneously, which makes the response speed slower. The second method is as follows Figure 5 As shown, a loop selection modulation block is involved which selects which of the various loops will control the modulation block based on a digital algorithm.

[0006] A first object of the present invention is to provide an analog control method for bidirectional power converters or programmable power supplies that will allow the converter current direction to be switched from forward to reverse in a seamless manner. Another object of the present invention is to provide an improved analog control method for bidirectional converters or programmable power supplies with a fast and seamless transition from one control mode to another, such as from voltage control to current limiting and reverse control. Another object of the present invention is to eliminate the tendency of boundary point oscillations between different control modes. Another object of the present invention is to eliminate or minimize the possibility of controlling dead zones in the forward or reverse direction at very low converter currents. Summary of the invention

[0007] The present invention includes the configuration and connection of multiple operational amplifiers (Operational Amplifiers, Op Amps) to create a high performance analog control circuit that can be used as part of a control system for a bidirectional converter or a bidirectional programmable controller. This circuit allows multiple control loops to exist simultaneously, while only one control loop is active at any particular time to control the converter. It overcomes the limitations of the prior art TL494 configuration in eliminating oscillations at the intersection between the two control loops and allowing control of a bidirectional converter with minimal control dead zone between the two directions of the converter. Similar to the TL494 circuit, it allows fast and seamless transfer between control loops, much faster than is possible using digital control methods such as the prior art digital control methods discussed. The controlled converter can be a non-isolated bidirectional converter (e.g. Figure 8 The buck or boost converter shown in FIG. 1 may also be an isolated converter (eg, a bidirectional phase-shifted full-bridge converter).

[0008] The present invention is particularly suitable for use with single or multiple parallel converters, each converter using an internal control loop, such as the average current control described by Lloyd Dixon in his article "Average Current Mode Control of Switching Power Supplies" ( Figure 6 ), or a charge control loop, as described in the ON Semiconductor NCP4390D IC datasheet. Multiple parallel converters are often used in high power or current programmable power supplies and can be operated at the same frequency but out of phase with each other to increase the power capability of the programmable power supply and reduce input and output ripple current and voltage. These individual converters can be controlled via average current mode control ( Figure 7 ) as described in the LM5170 datasheet. This control method ensures that the paralleled converters share the load current equally and prevents current recirculation between the converters. It should be noted that the circuit disclosed in the NCP4390DIC datasheet is only suitable for unidirectional converters, and the circuit disclosed in the LM5170 does not allow seamless control between the two directions of converter control, as is required in programmable power supplies, as a current direction control input is necessary.

[0009] One aspect of the present invention is a voltage error operational amplifier (Op Amp) having a resistor in series with its output. A low value capacitor is connected to the output of the operational amplifier, the resistance of which is just enough to prevent high frequency oscillations of the voltage error operational amplifier that may occur due to the presence of the series resistor. A second aspect of the present invention is a buffer operational amplifier, whose positive input is connected to one end of the series resistor and whose output is connected to its negative input to create a unity gain non-inverting buffer. is connected between the buffer operational amplifier output and the negative input of the voltage error operational amplifier. For better understanding, we refer to the output of the buffer operational amplifier as the buffer bus and its negative input as the loop bus. A large number of voltage error operational amplifiers and buffer operational amplifiers are powered by positive and negative auxiliary power supplies, in this case +5V and -5V respectively, to allow the operational amplifier input and output to have a bipolar range, and to facilitate the circuit signal common terminal (signal ground) to be grounded, that is, the bipolar range can be positive or negative relative to the common voltage point. The buffer bus is also the output signal of the converter current or charge control input, or it can be said that the signal conversion circuit of the required voltage ratio and offset adjustment operational amplifier can be added between the buffer bus and the converter control input.

[0010] A third aspect of the present invention is a number of other op amps, which we refer to as limiting op amps, whose outputs are connected to the loop bus via diodes connected in series with their outputs. These series connected diodes are polarized so that the function of a particular limiting op amp is to reduce the converter control voltage to zero volts. The forward voltage based on the diodes is typically 0.35V. The feedback network of these limiting op amps is connected from the buffer bus to the negative input of the corresponding op amp. Each of these op amps performs a unipolar limiting function such as forward current limiting, reverse current limiting, forward power limiting, reverse power limiting or reverse parallel resistance limiting. The current limiting op amp can be equivalent to a gain op amp with no capacitors used in its feedback network, only a resistor, because when used with an average current controlled converter, the circuit control output essentially determines the output current. The positive inputs of these limiting op amps are each connected to the appropriate reference voltage for the particular control loop, in this case the forward limiting op amp is connected to the positive polarity reference voltage and the reverse op amp is connected to the negative polarity reference voltage.

[0011] It is convenient to use a positive control voltage range for the forward direction of the converter and a negative control voltage range for the reverse direction, but the reverse direction can just as easily be used. It is also ideal to use rail-to-rail input and output op amps so that their outputs can go exactly to either supply voltage rail. In this case, the forward-limited op amp should be powered by a positive auxiliary supply and a negative voltage slightly negative than the forward conduction voltage of the series diode (e.g., -0.6V). Similarly, in this case, the reverse-limited op amp should be powered by a negative auxiliary supply and a positive voltage slightly higher than the forward conduction voltage of the series diode (e.g., +0.6V).

[0012] A fourth aspect of the invention is that these low voltage auxiliary supplies can be generated using simple circuits that are temperature compensated to match the temperature dependence of the forward conduction voltage of the series connected diodes. Thus, at low converter currents or power limiting reference voltages, the ability of the forward limiting op amp to compete with the reverse limiting op amp is limited by the resistance of the op amp output stage and the series diodes.

[0013] A fifth aspect of the present invention is a circuit for accurately adjusting the reference input of a current limiting unity gain operational amplifier to account for the inaccuracy of the average control loop of each average current mode or charge mode control converter and for implementing current limiting. A summing operational amplifier allows the error operational amplifier to adjust the current limit reference voltage to improve the accuracy of the programmable power supply current limit. When the off / on input goes low, the soft start circuit establishes a symmetrical ramp of current limit to implement the soft start function of the converter.

[0014] Adding an inverting configuration op amp circuit can be used to generate the negative polarity reference for the control mode from the positive polarity reference source. These can be differential op amps to improve accuracy and suppress noise and offset voltages between the reference source (usually a precision digital-to-analog converter) and the control circuit. Likewise, non-inverting differential op amps can be added to improve accuracy and suppress noise and offset voltages at the positive reference input. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 It is a circuit structure diagram of a control circuit of a bidirectional power converter disclosed in the first aspect, the second aspect and the third aspect of the embodiments of the present invention.

[0017] Figure 2This is a simplified circuit diagram of the prior art analog PWM control IC Silicon General (now Microchip) SG1524. The circuit diagram discloses two error amplifiers with their outputs connected directly together. The error amplifier on the left is the output voltage error amplifier, which is a transconductance amplifier. The current error amplifier is a low bandwidth, low gain differential amplifier with an input bias voltage of 200mV.

[0018] Figure 3 It is a simplified circuit diagram of the prior art analog PWM control ICTL494. This IC uses two conventional operational amplifiers as voltage and current error amplifiers, with the anodes of the diodes connected in series with their outputs, and the cathodes of the diodes connected together and pulled down by a constant current sink of 0.7mA.

[0019] Figure 4 is a logic block diagram of a prior art digital control method, which involves having a main voltage control loop that measures the output voltage Vs and subtracts it from the desired voltage set input Vset to produce a voltage error value, which is amplified by a transfer function Gv and then input to a pulse width modulator Kpwm. Various other control loops, such as a positive current loop with a gain Gc+, function to reduce the voltage setting input Vset of the voltage loop to limit the load current in the positive or negative direction. Therefore, the voltage control loop and another control loop are often active at the same time.

[0020] Figure 5 A loop selection block diagram of a prior art digital control method involving a loop selection block that selects which loop controls the modulation block based on an algorithm. If this were to be implemented in a physical circuit rather than a digital processor, comparators, logic, and switches would need to be used to create the algorithm.

[0021] Figure 6 is a simplified schematic of an average current mode controlled converter from the Lloyd Dixon article “Average Current Mode Control of Switching Power Supplies”.

[0022] Figure 7 The figure is a simplified diagram of the control method of the LM5170 average current control IC for a 2Phaseinterleaved bi-directional Buck or Boost converter.

[0023] Figure 8The system block diagram of a bidirectional power converter disclosed in an embodiment of the present invention is composed of several DC-DC converters connected in parallel, each of which has its own average current controller. The power supply output current is detected by a current shunt and its output voltage is detected by a voltage sense lead. Signal conditioning and calculation circuits process these inputs as well as various reference voltage inputs to provide appropriately scaled and polarized reference input voltages for analog control systems.

[0024] Fig. 9 A voltage and current diagram disclosed in an embodiment of the present invention is used to illustrate the working mode of a bidirectional programmable power supply.

[0025] Fig.10 It is a circuit structure diagram of an auxiliary power supply circuit disclosed in the fourth aspect of an embodiment of the present invention.

[0026] Fig.11 It is a circuit structure diagram of a fine-tuning circuit disclosed in the fifth aspect of an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1

[0029] The embodiment of the present invention discloses a control circuit of a bidirectional power converter, including a first aspect, a second aspect and a third aspect, and the basic schematic diagram is as follows: Figure 1 shown.

[0030] A first aspect of the present invention is a voltage error operational amplifier (Op Amp) 101 having a resistor 103 and a capacitor 104 connected in series, the first terminal of the resistor 103 being connected to the output of the voltage error operational amplifier, the first terminal of the capacitor 104 also being connected to the output of the voltage error operational amplifier, and its second terminal being connected to the negative input pin of the operational amplifier and having sufficient capacitance to prevent high frequency oscillations of the operational amplifier that may occur due to the presence of the series resistance. A voltage loop gain determining resistor 106 having a first terminal connected to the negative input of the voltage error operational amplifier 101 and having a second terminal connected to the output of a voltage sensing circuit that scales and buffers the output voltage of the converter for use in a control circuit. A voltage reference input 102 is connected to the positive input pin of the voltage error operational amplifier 101.

[0031] The second aspect of the present invention is a buffer op amp 107 having its positive input connected to the second terminal of the series resistor 103 and its output connected to its negative input to create a unity gain non-inverting voltage buffer. The first ends of the resistor and capacitor of the voltage loop feedback compensation network of the voltage error op amp 105 are connected to the output of the buffer op amp and the second ends thereof are connected to the negative input of the voltage error op amp. For better understanding, we will refer to the output of the buffer op amp as the buffer bus 115 and its negative input as the loop bus 114. Both the voltage error op amp 101 and the buffer error op amp 107 are powered by positive and negative auxiliary supplies, in this example +5V and -5V respectively, to allow both the op amp input and output to have bipolar ranges that can be positive or negative relative to a common voltage point that is most convenient for circuit signal common or signal ground. The voltage of the buffer bus 115 is also the output signal of the converter current or charge control input, although a separate buffer op amp can be used, it should be said that the required voltage ratio and offset adjustment op amps can be added between the buffer bus and the converter control input.

[0032] A third aspect of the invention is a plurality of other limiting op amps 108 whose outputs are connected to the loop bus 115 via series diodes 109, one terminal of each diode 109 being connected to one of the limiting op amp outputs and their second terminal being connected to the loop bus. These diodes are unipolar, so the role of a particular limiting op amp is to reduce the control voltage of the loop bus to zero volts. Ideally, these diodes will have a small forward voltage, so small signal Schottky diodes with a forward voltage of typically 0.35 volts are preferred. The compensation feedback network 111 of these op amps must have some series resistance, the first terminal of each compensation feedback network 111 is connected to the buffer bus, and their second terminal is connected to the negative input of the corresponding op amp. Each of these op amps performs a unipolar limiting function, such as forward current limiting, reverse current limiting, forward power limiting, reverse power limiting, or reverse parallel resistance limiting. The current limiting op amps can be configured as unity gain op amps with no capacitors in their feedback compensation network, just like average current controlled converters, and their output current is proportional to the control circuit control voltage. For a non-unity gain limiting operational amplifier 108 , a first terminal of the gain control resistor 113 is connected to the negative input of the operational amplifier 108 , and a second terminal thereof is connected to a suitable output sampling circuit, such as an output power sampling circuit, or a current sampling circuit.

[0033] It is convenient to use the positive control voltage range as the forward operation of the converter, although the opposite voltage range can be easily used as well, and it is best to use rail-to-rail input and output op amps so that their outputs can accurately conduct to either supply voltage. In this case, the forward limiting op amp should be powered by a substantially positive auxiliary supply and a negative voltage that is substantially no more negative than the forward conduction voltage of the series-connected diodes (e.g., -0.6V). Similarly, the reverse limiting op amp should be powered by a substantially negative auxiliary supply and a positive voltage that is substantially no more positive than the forward conduction voltage of the series-connected diodes (e.g., +0.6V). Appropriate unipolar input clamping diodes 112 are also connected to the negative input of each limiting op amp 108 so that these inputs do not exceed the common mode range of the op amp during transient conditions. The positive input of each of these limiting op amps is connected to an appropriate reference voltage 110 for the particular control loop, and in this case, the forward limiting op amp is connected to the positive polarity reference voltage, while the reverse op amp is connected to the negative polarity reference voltage.

[0034] Figure 8 A block diagram of a partially programmable power supply consisting of a plurality of parallel connected DC-DC converters 1, each converter containing its own average current controller, is shown. The DC-DC converter has a power supply input 2 and a load output 3 across its output capacitor 4. A signal conditioning and calculation circuit block 7 processes these inputs as well as various reference voltage inputs 9 to provide appropriately scaled and polarity processed reference input voltages to the analog control system 10 which is the subject of the present invention. A negative polarity reference for the reverse limiting operational amplifier is generated from a positive polarity reference source, which may be a differential operational amplifier to improve accuracy and suppress noise and offset voltages between the reference sources (typically precision digital / analog converters). Similarly, a non-inverting differential operational amplifier may be added to circuit block 7 to improve accuracy and suppress noise and offset voltages as a reference for the forward limiting operational amplifier. This block should also include a multiplier to calculate the output power of the programmable power supply, and in the case of a reverse constant resistance limiting operation using a reference input; a circuit to multiply the output voltage by the constant resistance reference voltage. A signal conversion circuit block 11 scales and level shifts the current control signal to the requirements of the control input of the converter average current control circuit.

[0035] The novelty and working principle of this circuit are explained as follows: Fig. 9A diagram showing the operating modes of a bidirectional DC programmable power supply (PPS) is shown. The primary operating mode is the constant voltage mode (CV) where the control circuit will maintain the output voltage constant regardless of whether the load current is coming from the PPS (forward) or being sunk by the PPS (reverse). The PPS will have a maximum output voltage Vmax and a CV regulation point Vset that is adjustable from zero volts to Vmax. The PPS will also have maximum forward and reverse current limits +Imax and -Imax, power limits +Pmax and -Pmax, and adjustable set points +Iset, -Iset, +Pset, and -Pset that can also be adjusted from near zero to maximum values ​​to achieve forward and reverse constant current (CC) and constant power (CP) modes. In addition, a DCPPS typically has a parallel reverse constant resistance mode (CR) mode that can be adjusted from a minimum value Rmin to infinity. A series forward CR mode is also possible, which is not the subject of this document. The output operation of the PPS needs to be regulated by the control circuit to be exactly at one of the regulation set points of one of the modes at any time and to quickly and seamlessly transition from one mode to another without oscillating at the boundaries between the various modes. Figure 1The described analog control circuit achieves this by having an output voltage error operational amplifier (OpAmp) having a first terminal of a resistor 103 connected to its output terminal and a second terminal of a resistor connected to an Oring bus 114. The voltage of the loop bus is used to control the output current of the PPS converter, and if the controlled converters all use an average current control loop, this voltage is proportional to the output current value. The outputs of the limiting operational amplifiers of the other control modes are connected to this second terminal of the resistor 103 via a series and appropriately polarized diode 109 so that they can make the control voltage close to zero volts to adjust the output current set point of each other control mode. The second novelty of the present invention is that a buffer operational amplifier 107 is placed between the loop bus 114 and the buffer bus 115, and all compensation feedback networks 105 and 111 of all control mode operational amplifiers including the voltage error operational amplifier are connected to the buffer operational amplifier 107. This prevents the compensation feedback networks 105 and 111 from affecting the voltage of the loop bus, and the low output impedance of the buffer operational amplifier 107 also effectively decouples the compensation feedback networks from each other. When one of the limiting error operational amplifiers 108 other than the voltage error operational amplifier 101 is controlling the converter current, the error voltage operational amplifier 101 outputs a voltage that reaches one of its auxiliary supply voltage rails, so it no longer controls the converter output current. Since the compensation feedback networks 105 and 111 are not driven by the error operational amplifiers, the output voltages of all error operational amplifiers can switch very quickly and are only limited by their specified switching rates, so that the control circuit can change from one control mode to another. This greatly reduces the overshoot of the converter output voltage and current when the control mode switches from one mode to another. Since the loop bus 114 is not loaded by the various compensation feedback networks, and since the low output impedance of the buffer operational amplifier effectively isolates the networks from each other, oscillations at the boundaries between modes are eliminated. A third novelty of the present invention is that the opposite auxiliary supply voltages of the forward and reverse limiting error operational amplifiers (CC, CP, and CR) are adjusted to be only sufficiently greater than the forward conduction voltage of the series diodes connected in series therewith. When the mode setting value is close to zero volts, conflicts between the forward and reverse limiting operational amplifiers are prevented. The series connected diode and the resistance of the op amp output stage will be sufficient to limit the conflicting current to less than the current that the controlling error op amp can source or sink. For example, when the converter is operating in forward direction and one of the limiting op amps is controlling the converter's output current, the error op amp output will be at its positive auxiliary supply voltage and only the positive limiting op amp can limit the control voltages of the loop bus and the buffer bus.

[0036] Embodiment 2

[0037] A fourth aspect of the present invention is a circuit for generating a small value auxiliary supply voltage for forward and reverse limiting an operational amplifier, such as Fig.10 as shown. Bias diodes 201. The values ​​of the resistors must be low enough so that the current flowing through them is greater than the current required by the auxiliary power supply pins of all the connected operational amplifiers. The diodes must have a slightly higher forward conduction voltage than the series-connected diodes 109, so it is best to use silicon diodes. The type of diode can be selected to achieve the required auxiliary supply voltage, for example 0.6V. Capacitors 203 act as filtering and energy storage components for the auxiliary supplies to ensure that their voltage has minimal ripple and noise. One advantage of this type of low voltage auxiliary supply circuit is that these auxiliary supply voltages will change with temperature to match the temperature-dependent forward voltage of the series-connected diodes 109, because these auxiliary voltages are determined by the temperature-dependent forward conduction voltage of the diodes 109.

[0038] Embodiment 3

[0039] The fifth aspect of the present invention is a circuit for accurately adjusting the reference input of a current-limiting unity-gain operational amplifier to solve the inaccuracy of the average control loop of each average current mode or charging mode control converter and to achieve current limiting. Two current-limiting adjustment operational amplifiers 301 compare the actual sensed output current signal with the current-limiting reference voltage. The first terminal of the feedback compensation network 302 is connected to the corresponding output pins of these operational amplifiers, and its second terminal is connected to the negative input pin. The first terminal of the gain resistor 303 is connected to the corresponding adjustment operational amplifier negative input pin, and their second terminal is connected to the low-impedance signal of the sensed output current. The first terminal of the voltage divider network 304 is connected to the corresponding current limit reference signal, the second terminal is connected to the positive input of the corresponding current limit adjustment operational amplifier, and the third terminal is connected to the signal common reference point. The output of the current-limiting adjustment operational amplifier is connected to the first input of the appropriate summing operational amplifier 305. The second input of each summing operational amplifier 305 is connected to the corresponding current-limiting reference voltage input of the circuit. The input gain of the summing operational amplifier from the error operational amplifier should be low, such as -5%, so the operational amplifier can only fine-tune the current reference voltage, and the input gain from the current reference voltage is usually -1. A first terminal of resistor 306 is connected to the output of the summing operational amplifier and a second terminal of resistor 306 is connected to the corresponding regulated current limit reference output of the circuit. A soft start capacitor 307 is initially discharged by a switching device 309 upon receiving a low switch input signal and is charged by a first terminal of a small current source 308, which may be a high value resistor and whose second terminal is connected to a higher value auxiliary supply voltage, such as 15V. A unity gain non-inverting operational amplifier 310 also has its positive input pin connected to the soft start capacitor 307 and its output pin connected to the output pin of the non-inverting unity gain operational amplifier 310 through a first terminal of a low forward voltage diode 311 and its second terminal, which is polarized so as to pull the regulated forward current limit reference output down to zero volts when the soft start capacitor is discharged. A unity gain inverting operational amplifier 312 also has its negative input connected to the output pin of the buffer operational amplifier 310 through a series resistor. The second terminal is connected to the reverse current limit adjustment reference output, and the diode is polarized so as to pull the reverse current limit adjustment reference output up to zero volts when the soft start capacitor is discharged. In this way, a symmetrical slope of the current limit can be achieved after the off / on input goes low, thus achieving the soft start function of the converter. It should be noted that since the summing op amp is essentially an inverting configuration, a current reference signal of opposite polarity is required to be input to this circuit.A preferably differential inverting operational amplifier type may be part of the signal conditioning and computation circuit block 7 and is used to generate a negatively polarized current reference signal for the forward current limit reference adjustment circuit from a unipolar positive reference source, while the reference input for the reverse current limit may be handled by a non-inverting operational amplifier, also preferably a differential type operational amplifier.

[0040] Embodiment 4

[0041] An embodiment of the present invention discloses a control system for a bidirectional power converter, including a control circuit of a bidirectional power converter as described in Example 1, a circuit for generating a small auxiliary power supply voltage for a forward and reverse limiting operational amplifier as described in Example 2, and a circuit for accurately adjusting the reference input of a current limiting unit gain operational amplifier as described in Example 3.

[0042] The contents disclosed in the embodiments of the present invention only disclose the preferred embodiments of the present invention, which are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it should be understood by those skilled in the art that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control system for a bidirectional power converter, comprising a control circuit for controlling a bidirectional DC-DC converter, characterized in that: The control circuit includes a voltage error operational amplifier, a resistor, a first capacitor, a plurality of diodes and a plurality of limiting operational amplifiers; the voltage error operational amplifier is used to compare the output voltage of the converter with a reference voltage; the first end of the resistor is connected to the output end of the voltage error operational amplifier; the first capacitor is connected between the output end of the voltage error operational amplifier and the negative input end of the voltage error operational amplifier; the first ends of the plurality of diodes are connected to the second end of the resistor, and the second end of each of the diodes is connected to the output end of the corresponding limiting operational amplifier, so that at least one diode is connected in series with its corresponding operational amplifier output and is polarized according to the function of the corresponding limiting operational amplifier, and the function limits the output current of the limiting operational amplifier to the forward direction of the converter current or the reverse direction of the converter current.

2. The control system according to claim 1, characterized in that: Each of the limiting operational amplifiers is associated with a corresponding feedback compensation network, and further comprises a unity gain non-inverting buffer operational amplifier having a positive input terminal connected to the second end of the resistor and an output terminal connected to a negative input terminal of the buffer operational amplifier and to a terminal of at least one of the feedback compensation networks, and wherein an output terminal of the buffer operational amplifier provides an output signal to control a current in the converter.

3. The control system according to claim 2, characterized in that: The output of the buffer operational amplifier is also connected to a terminal of a voltage error operational amplifier feedback compensation network.

4. The control system according to claim 3, characterized in that: At least one of the limiting operational amplifiers has a first input connected to a voltage reference, and one terminal of a feedback resistor connected to a negative input terminal of the at least one operational amplifier and another terminal of the at least one operational amplifier.

5. The control system according to claim 3, characterized in that: At least one negative input terminal of the limiting operational amplifier is connected to a signal representing the output of the converter, so that the circuit implements at least one of the functional groups selected from the following groups: the output functions of the converter include forward current limiting, reverse current limiting, forward power limiting, reverse power limiting and reverse constant resistance limiting.

6. The control system according to claim 3, characterized in that: The operational amplifier is a rail-to-rail input and output type operational amplifier.

7. The control system according to claim 3, characterized in that: The diode is a small signal Schottky diode.

8. The control system according to claim 3, characterized in that: The auxiliary power supply pins of the voltage error operational amplifier and the buffer operational amplifier are connected to an auxiliary power supply voltage, the value of the auxiliary power supply voltage is such that the input and output voltage operational amplifiers of the voltage error operational amplifier and the buffer allow control of the forward direction of the converter output current and the reverse direction of the converter output current in the DC-DC converter.

9. The control system according to claim 1, characterized in that: The auxiliary power supply pin of each of the limiting operational amplifiers is connected to an auxiliary voltage, the value of the auxiliary voltage is selected so that each of the limiting operational amplifiers can only limit the converter output in one direction, and so that the converter output current can be controlled to a negligible value through each of the limiting operational amplifiers.

10. The control system according to claim 1, characterized in that: wherein the auxiliary supply voltages on the auxiliary supply pins are sufficiently different to provide a control range for limiting the forward direction of the output current of the DC-DC converter, and wherein the voltage values ​​on the auxiliary supply pins are not substantially greater than the forward conduction voltage of a first one of the auxiliary supply pins.

11. The control system according to claim 3, characterized in that: The negative input pin of the limiting operational amplifier is protected from a voltage exceeding its common mode range by a suitably polarized low forward clamping diode connected to the negative input pin of the limiting operational amplifier, and the other terminal of the negative input pin of the limiting operational amplifier is connected to a signal ground or a signal common terminal.

12. The control system according to claim 11, characterized in that: The feedback resistor or the feedback compensation network has a resistance value that is selected such that the current capability of the diode and the output of the buffer operational amplifier is not exceeded.

13. The control system according to any one of claims 1 to 12, characterized in that: It also includes a circuit for providing an auxiliary power supply voltage for one or more of the limiting operational amplifiers, each limiting operational amplifier having a series diode connected to the output terminal of the limiting operational amplifier, including a polarized diode having a forward conduction voltage greater than the forward conduction voltage of the series diode, one end of which is connected to a signal common terminal, and the other terminal of the diode is connected to a first terminal of a resistor, the resistor is used as a current source for forward biasing the polarized diode, the second terminal of the resistor is connected to the main power supply auxiliary power supply, and a second capacitor is connected in parallel with each of the polarized diodes.

14. The control system according to any one of claims 1 to 12, characterized in that: Also included is a circuit for generating an adjusted reference voltage for forward or reverse current limiting in the control circuit, including first and second operational amplifiers, the first operational amplifier generating an output proportional to the difference between the forward current references, the inverting summing operational amplifier summing the forward current limit reference input and the output of the second operational amplifier, and two inverting summing operational amplifiers summing the reverse current limit reference input and the output of the second operational amplifier.

15. The control system according to claim 14, characterized in that: The circuit also has a bidirectional current soft-start function: it also includes a third capacitor, one terminal of the third capacitor is connected to the signal ground or the signal common terminal, and the second terminal of the third capacitor is connected to the first terminal of the current source, the second terminal of the current source is connected to the main auxiliary power supply voltage, the third capacitor is connected in parallel with a switching device configured to selectively discharge the third capacitor, a non-inverting operational amplifier having a negative input terminal connected to its output terminal and a positive input terminal connected to an inverting operational amplifier of the third capacitor, its negative input is connected to the output of the non-inverting operational amplifier, and its positive input is connected to the signal ground or the signal common terminal, a first diode having a terminal connected to the output of the non-inverting operational amplifier and polarized to pull the value of the adjusted current reference voltage toward zero, and a second diode having a terminal connected to the output of the inverting operational amplifier and polarized to pull the value of the adjusted current reference voltage toward zero.

16. The control system according to claim 3, characterized in that: Each of the feedback compensation networks includes at least one resistor, or at least one resistor and at least one capacitor.

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