Power UPS (Uninterrupted Power Supply) with input direct current double frequency ripple suppression

Abstract

The invention relates to a power UPS (Uninterrupted Power Supply) with input direct current double frequency ripple suppression. The power UPS comprises an input isolation transformer, a PFC (Power Factor Correction) circuit, a battery assembly with a switch and a DC / AC (Direct Current / Alternating Current) circuit, the PFC circuit comprises a rectifier bridge and a Boost circuit, the input side of the input isolation transformer is connected with alternating current, the output side of the input isolation transformer is connected with the rectifier bridge, the output side of the rectifier bridge is firstly connected with a battery assembly with an output switch in parallel and then connected into the Boost circuit, and the output of the Boost circuit is connected with the DC / AC circuit; the AC / DC conversion loop during alternating current power supply and the DC / DC conversion loop during battery power supply share the Boost circuit, and double frequency ripple is suppressed by combining the double frequency ripple suppression control ring. The method has the advantages that the double-frequency ripple current can be rapidly suppressed, and the test results of double-frequency starting impact current and double-frequency backward irrigation ripple voltage indexes are excellent.

Description

Technical Field

[0001] The invention relates to the field of uninterruptible power supply, in particular to an electric power UPS with input direct current double frequency ripple suppression. Background Art

[0002] The integrated power supply system of 50kv, 110kv and above substations has very high requirements for the reliability and performance indicators of the power UPS (Uninterruptible Power Supply). The integrated power supply system mainly includes a DC operating power supply and a power UPS. The DC operating power supply output is used as the system common DC bus, and many important power-taking devices, including UPS, are hung on the DC bus. The UPS DC input is connected to the DC bus, so the input characteristics of the UPS will seriously affect the stability of the DC bus. The most important indicators on the DC input side include the starting impact current and the reverse ripple voltage of the UPS. The starting impact current refers to the ratio of the maximum impact current to the stabilized current under rated conditions, which should not exceed 150%; the reverse ripple voltage refers to the ratio of the effective value of the ripple voltage to the average value of the DC voltage under rated conditions, which should be less than 0.5%.

[0003] The main solutions adopted by traditional power frequency UPS are as follows: Figure 1 As shown in the figure, the AC input adopts the scheme of uncontrolled rectification after resistor slow start, and the battery is directly connected to the busbar. The system must be equipped with a bulky double frequency filter to deal with it. The AC input power factor and current harmonic distortion rate of this scheme are both low. The improved substation power UPS solution with PFC is shown in the figure. Figure 2 As shown, it can effectively improve the power factor and current harmonic distortion rate of AC input, but the DC side still maintains the traditional battery direct hanging scheme. In the traditional scheme, the DC input index is suppressed by connecting inductors L4 and L5 in series on the DC side and adding capacitor C1 to the busbar. However, as the rated voltage of the battery decreases, the number of inductors and capacitors in series also needs to be larger. This method not only has limited effect but also has relatively high cost. In short, the existing substation power UPS adopts an input and output dual isolation power frequency transformer structure, such as Figure 1 , Figure 2 The DC side of the UPS uses a battery directly connected to the DC bus solution, and the input electrical performance indicators are poor. To meet the latest industry standards, many additional components are required, resulting in no cost advantage. Summary of the invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide an electric power UPS with input DC current double frequency ripple suppression, which can quickly suppress the double frequency ripple current, and the test results of the double frequency starting impact current and the double frequency feedback ripple voltage indicators are excellent.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] An electric UPS with input DC current double frequency ripple suppression comprises an input isolation transformer, a PFC circuit, a battery assembly with a switch and a DC / AC circuit; the PFC circuit comprises a rectifier bridge and a Boost boost circuit, the input side of the input isolation transformer is connected to AC power, and the output side is connected to the rectifier bridge, the output side of the rectifier bridge is first connected in parallel with the battery assembly and then in parallel with the Boost boost circuit, and the output of the Boost boost circuit is connected to the DC / AC circuit; when powered by AC, the switch is disconnected, and when powered by battery, the switch is connected, and the AC / DC conversion circuit when powered by AC and the DC / DC conversion circuit when powered by battery share the Boost boost circuit.

[0007] More preferably, the double frequency ripple suppression control loop of the electric power UPS includes voltage loop control, current loop target waveform monitoring and current loop control. The voltage loop control stabilizes the bus voltage at a given bus voltage value. The current loop target waveform monitoring is used to switch the inductor current given value of the current loop. The current loop control stabilizes the inductor current in the Boost circuit at the given inductor current value. The output of the current loop is the duty cycle of the Boost circuit.

[0008] Preferably, step 1, the voltage loop control step is as follows: sampling the bus voltage, the sampling signal is U bus (k), bus voltage given value U ref (k) and the sampling voltage U bus (k), the error value Err_v(k) is input to the first PID controller, and the output is the voltage loop output value, which is the current loop peak value I ref_peak (k), the operation formula of the first PID controller is as follows: Among them, K p_v is the voltage loop proportional coefficient, K i_v is the voltage loop integral coefficient, k is the discretized sampling point;

[0009] Step 2: The current loop target waveform monitoring steps are as follows: Sampling the AC voltage, the sampling signal is U ac (k), determine the AC voltage U ac (k) Is it abnormal? If it is abnormal, the UPS works in DC power supply mode, then the inductor current set value I in the current loop ref (k) is 1*I ref_peak (k); If the AC voltage is normal and the UPS works in AC power supply mode, the inductor current given value I in the current loop ref(k) is |U ac (k)|*I ref_peak (k)*Gain, where the coefficient Gain is used to convert |U ac (k)| is calibrated to the range [0,1]; the formula is as follows:

[0010]

[0011] Step 3: The current loop control steps are as follows: Sampling the inductor current, the sampling signal is I induct (k), given value of inductor current I ref (k) and sampling current I induct (k), the error value Err_i(k) is input to the second PID controller, and the output is the current loop output value, that is, the duty cycle D(k) for driving the DC / AC circuit. The operation formula of the second PID controller is as follows:

[0012]

[0013] Among them, K p_i is the current loop proportionality coefficient, K i_i is the current loop integral coefficient and k is the discretized sampling point;

[0014] Repeat steps 1 to 3 until the bus voltage U sampled in the voltage loop is bus (k) Stable at the bus voltage given value U ref (k), the double frequency ripple suppression control loop reaches steady state.

[0015] More preferably, the Boost circuit includes an inductor, a switch tube, a diode and a filter capacitor; the output end of the rectifier bridge is connected in parallel with the battery and the switch connected in series, one end of the inductor is connected to the output end of the rectifier bridge, and the other end is respectively connected to the diode and the switch tube, the other end of the diode is connected to the filter capacitor, the negative electrode of the battery, the switch tube and the filter capacitor are grounded, the DC / AC circuit is connected in parallel to the filter capacitor, and the filter capacitor serves as a bus capacitor.

[0016] More preferably, the battery assembly includes a battery and a switch connected in series, and the switch is a thyristor.

[0017] More preferably, the DC / AC circuit includes an inverter, and an input end of the inverter is connected in parallel to the filter capacitor.

[0018] More preferably, the DC / AC circuit further includes an output isolation transformer, the output end of the inverter is further connected to an output isolation transformer, and the output isolation transformer is connected to a load.

[0019] The present invention has the following beneficial effects:

[0020] In terms of circuit topology, the present invention uses a common Boost circuit for DC / DC conversion of DC input and AC / DC conversion of PFC (power factor correction loop). The digital control strategy also integrates the PFC modulation loop and the control loop technology of double-frequency ripple suppression, and optimizes the control program code. It can not only suppress the double-frequency ripple on the DC side to achieve a lower DC double-frequency ripple current index, but also achieve relatively excellent UPS AC input power factor and harmonic current and other indicators, and has a great cost advantage. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of a conventional substation power UPS circuit without PFC in the prior art;

[0022] Figure 2 It is a schematic diagram of the circuit of a substation power UPS with PFC after improvement in the prior art;

[0023] Figure 3 Another schematic block diagram of the circuit structure of the electric power UPS of the present invention;

[0024] Figure 4 It is a circuit schematic diagram of the electric power UPS of the present invention;

[0025] Figure 5 It is a schematic diagram of the double frequency ripple suppression control loop of the present invention;

[0026] Figure 6 This is the test effect diagram of using the existing 3kVA UPS with inductance in series on the DC side;

[0027] Figure 7 The figure is a test effect diagram of the inductor connected in series on the DC side using the UPS of the present invention. DETAILED DESCRIPTION

[0028] See also Figure 3, an electric UPS with input DC current double frequency ripple suppression, including an input isolation transformer, a PFC circuit, a battery assembly with a switch, and a DC / AC circuit. The PFC circuit includes a rectifier bridge and a Boost boost circuit. The input side of the input isolation transformer is connected to AC power, and the output side is connected to the rectifier bridge. The input isolation transformer plays the role of input voltage reduction and isolation. The output side of the rectifier bridge is first connected in parallel with the battery assembly and then in parallel with the Boost boost circuit, and the output of the Boost boost circuit is connected to the DC / AC circuit. The battery assembly includes a battery and a switch connected in series, and the switch can preferably be a thyristor. When AC power is supplied, the switch is disconnected, and the PFC circuit realizes AC / DC conversion. When AC is abnormally disconnected, the switch is turned on. When the battery provides DC power, the Boost boost circuit realizes DC / DC conversion, and the thyristor controls whether the UPS works in AC power supply mode or battery power supply mode. When the UPS works in any mode, the Boost boost circuit is shared in the circuit topology. The circuit topology of the present invention also omits the large inductance and large capacitance that must be used when the battery is directly hung on the busbar in the prior art, thereby reducing the number of components used and saving equipment costs.

[0029] The turns ratio N of the input isolation transformer can be optimally adjusted according to different rated DC voltage requirements.

[0030] The DC / AC circuit includes an inverter, the input end of which is connected in parallel to the filter capacitor, and the inverter converts direct current into alternating current. In this embodiment, an output isolation transformer can be connected after the inverter according to the voltage requirement of the load to achieve AC / DC electrical isolation. A suitable transformer turns ratio N can allow different DC voltage inputs to meet the load power supply voltage requirement.

[0031] The boost circuit includes an inductor, a diode, a switch tube and a filter capacitor. The filter capacitor is used as a DC bus capacitor. The voltage across the filter capacitor is the bus voltage, which is common knowledge in the art. Figure 4 The circuit topology of the Boost circuit in this embodiment is described as follows: the output end of the rectifier bridge is connected in parallel with the battery and the switch connected in series, one end of the inductor L3 is connected to the output end of the rectifier bridge, and the other end is connected to the diode D3 and the switch tube Q5 respectively, the other end of the diode D3 is connected to the filter capacitor C1, the negative electrode of the battery BAT, the switch tube Q5 and the filter capacitor C1 are grounded, the DC / AC circuit is connected in parallel to the filter capacitor C1, and the filter capacitor C1 serves as a bus capacitor.

[0032] Based on the above circuit topology, the software control strategy integrates the PFC loop and the double frequency ripple suppression control loop. The double frequency ripple suppression control loop of the power UPS includes voltage loop control, current loop target waveform monitoring and current loop control. The voltage loop control is to stabilize the bus voltage at a given bus voltage value. The current loop target waveform monitoring is used to switch the control target of the current loop. In this embodiment, the control target of the current loop is a given value of the inductor current. When the AC is abnormal, the UPS is powered by a battery, and the current loop is stabilized to a DC waveform. When the AC is normal, the UPS is powered by AC, and the current loop stabilizes to a half-sine wave waveform, and the frequency is twice the AC frequency. The current loop control is to stabilize the inductor current in the Boost boost circuit at the given value of the inductor current. The output of the current loop is the drive duty cycle of the BOOST circuit. The control block diagram is shown in FIG. Figure 5 As shown in the figure, k is the AC voltage calibration coefficient, abs is the absolute value function, and the specific execution process is as follows:

[0033] Step 1: The voltage loop control steps are as follows: Sampling the bus voltage, the sampling signal is U bus (k), bus voltage given value U ref (k) and the sampling voltage U bus (k) is subtracted, and the error value Err_v(k) is input into the first PID controller G v (s), the output is the voltage loop output value, which is the current loop peak value I ref_peak (k), the first PID controller G v The calculation formula of (s) is as follows:

[0034] Among them, K p_v is the voltage loop proportional coefficient, K i_v is the voltage loop integral coefficient, k is the discretized sampling point;

[0035] Step 2: The current loop target waveform monitoring steps are as follows: Sampling the AC voltage, the sampling signal is U ac (k), determine the AC voltage U ac (k) Is it abnormal? If it is abnormal, the UPS works in DC power supply mode, then the inductor current set value I in the current loop ref (k) is 1*I ref_peak (k); If the AC voltage is normal and the UPS works in AC power supply mode, the inductor current given value I in the current loop ref (k) is |U ac (k)|*I ref_peak (k)*Gain, where the coefficient Gain is used to convert |U ac (k)| is calibrated to the range [0,1]. The formula is as follows:

[0036]

[0037] Step 3: The current loop control steps are as follows: Sampling the inductor current, the sampling signal is I induct (k), given value of inductor current I ref (k) and sampling current I induct (k), the error value Err_i(k) is input to the second PID controller G i (s), the output is the current loop output value, that is, the duty cycle D(k) of driving the DC / AC circuit, and the second PID controller G i The calculation formula of (s) is as follows:

[0038] Among them, K p_i is the current loop proportionality coefficient, K i_i is the current loop integral coefficient and k is the discretized sampling point;

[0039] Repeat steps 1 to 3 until the bus voltage U sampled in the voltage loop is bus (k) Stable at the bus voltage given value U ref (k), the double frequency ripple suppression control loop reaches steady state.

[0040] When the novel power topology structure and double frequency ripple suppression method proposed in the present invention are applied to the substation power UPS, the double frequency ripple current can be quickly converged into a DC waveform, the double frequency ripple current of the DC input approaches zero, and the test start-up impact current and reverse ripple voltage indicators are both effective. Taking the 3kVA UPS power supply as an example, two groups of experiments were performed at rated full load. Figure 6 As shown in the figure, it is the experimental waveform of the DC input string with 6mH inductor, channel 1 is the bus voltage, channel 2 is the DC input current, channel 3 is the inverter voltage, channel 4 is the DC input voltage, the DC side current is pulsating at twice the frequency, the maximum current is 22.4A, and the average current is 13.115A; Figure 7 As shown, it is the experimental waveform of this patent, channel 1 is the bus voltage, channel 2 is the DC input current, channel 3 is the inverter voltage, channel 4 is the DC input voltage, the inductor current is almost flat, the maximum current is 15.6A, the average current is 13.337A, and the effect is excellent.

[0041] In summary, the DC side of the present invention can not only suppress the double frequency ripple of the DC input to achieve a lower DC double frequency ripple current index, but also achieve relatively excellent UPS AC input power factor and harmonic current and other indicators, and has a great cost advantage.

[0042] The above description is only a specific implementation mode of the present invention, and does not limit the patent scope of the present invention. Any equivalent structural transformation made by using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An electric UPS with input DC current double frequency ripple suppression, characterized in that: It includes an input isolation transformer, a PFC circuit, a battery assembly with a switch and a DC / AC circuit; the PFC circuit includes a rectifier bridge and a Boost boost circuit, the input side of the input isolation transformer is connected to AC power, and the output side is connected to the rectifier bridge, the output side of the rectifier bridge is first connected in parallel with the battery assembly and then in parallel with the Boost boost circuit, and the output of the Boost boost circuit is connected to the DC / AC circuit; when powered by AC, the switch is disconnected, and when powered by the battery, the switch is connected; the AC / DC conversion circuit when powered by AC and the DC / DC conversion circuit when powered by the battery share the Boost boost circuit.

2. The power UPS with input DC current double frequency ripple suppression according to claim 1, characterized in that: The double frequency ripple suppression control loop of the electric power UPS includes voltage loop control, current loop target waveform monitoring and current loop control. The voltage loop control is to stabilize the bus voltage at a given bus voltage value. The current loop target waveform monitoring is used to switch the inductor current given value of the current loop. The current loop control is to stabilize the inductor current in the Boost circuit at the given inductor current value. The output of the current loop is the duty cycle of the boost circuit.

3. The power UPS with input DC current double frequency ripple suppression according to claim 2, characterized in that: Step 1: The voltage loop control steps are as follows: Sampling the bus voltage, the sampling signal is U bus (k), bus voltage given value U ref (k) and the sampling voltage U bus (k), the error value Err_v(k) is input to the first PID controller, and the output is the voltage loop output value, which is the current loop peak value I ref_peak (k), the operation formula of the first PID controller is as follows: Among them, K p_v is the voltage loop proportional coefficient, K i_v is the voltage loop integral coefficient, k is the discretized sampling point; Step 2: The current loop target waveform monitoring steps are as follows: Sampling the AC voltage, the sampling signal is U ac (k), determine the AC voltage U ac (k) Is it abnormal? If it is abnormal, the UPS works in DC power supply mode, then the inductor current set value I in the current loop ref (k) is 1*I ref_peak (k); If the AC is normal and the UPS works in AC power supply mode, the inductor current given value I in the current loop ref (k) is |U ac (k)|*I ref_peak (k)*Gain, where the coefficient Gain is used to convert |U ac (k)| is calibrated to the range [0, 1]; the formula is as follows: Step 3: The current loop control steps are as follows: Sampling the inductor current, the sampling signal is I induct (k), inductor current given value I ref (k) and sampling current I induct (k), the error value Err_i(k) is input to the second PID controller, and the output is the current loop output value, that is, the duty cycle D(k) for driving the DC / AC circuit. The operation formula of the second PID controller is as follows: Among them, K p_i is the current loop proportionality coefficient, K i_i is the current loop integral coefficient, k is the discretized sampling point; Repeat steps 1 to 3 until the bus voltage U sampled in the voltage loop is bus (k) Stable at the bus voltage given value U ref (k), the double frequency ripple suppression control loop reaches steady state.

4. The electric power UPS with input DC current double frequency ripple suppression according to claim 1, characterized in that: The Boost circuit includes an inductor, a switch tube, a diode and a filter capacitor; the output end of the rectifier bridge is connected in parallel with the battery and the switch connected in series, one end of the inductor is connected to the output end of the rectifier bridge, and the other end is respectively connected to the diode and the switch tube, the other end of the diode is connected to the filter capacitor, the negative electrode of the battery, the switch tube and the filter capacitor are grounded, the DC / AC circuit is connected in parallel to the filter capacitor, and the filter capacitor serves as a bus capacitor.

5. The electric power UPS with input DC current double frequency ripple suppression according to claim 1, characterized in that: The battery assembly comprises batteries and switches connected in series, and the switch is a thyristor.

6. The electric power UPS with input DC current double frequency ripple suppression according to claim 1, characterized in that: The DC / AC circuit includes an inverter, and the input end of the inverter is connected in parallel to the filter capacitor.

7. The electric power UPS with input DC current double frequency ripple suppression according to claim 6, characterized in that: The DC / AC circuit further includes an output isolation transformer. The output end of the inverter is also connected to an output isolation transformer, and the output isolation transformer is connected to a load.

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