Doubling width-modulated inverter
The UDShM UPS inverter circuit addresses conductive losses and failure rates in UPS systems by distributing current across two valves and reducing connections, achieving efficient and reliable power supply.
Patent Information
- Authority / Receiving Office
- RU · RU
- Patent Type
- Patents
- Current Assignee / Owner
- OBSHCHESTVO S OGRANICHENNOJ OTVETSTVENNOSTYU NPP LM INVERTOR
- Filing Date
- 2025-08-18
- Publication Date
- 2026-06-30
AI Technical Summary
Existing UPS inverter circuits suffer from significant conductive power losses and increased failure rates due to the operating current passing through two series-connected transistors, especially in high-power applications, and two-stage structures exacerbate these issues with numerous connections and increased fault likelihood.
A new UPS inverter circuit using a UDShM configuration with two three-phase bridges, a three-winding transformer, and a constant voltage capacitor bank, where the battery is connected between the rectifier windings, distributing battery current across two valves in alternate half-cycles, reducing conductive losses and fault susceptibility.
The UDShM circuit nearly halves the valve current and conductive losses, reduces heating, and lowers the failure rate by minimizing connections without isolation, making it suitable for critical power supply applications.
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Abstract
Description
[0001] The invention relates to electrical engineering, primarily to inverters for powerful static uninterruptible power supply units, which, when the main power source (public grid, three-phase alternating current generator) fails to operate, supply power to critical consumers, such as power supply systems of nuclear power plants, by converting direct current electricity stored in a storage battery (AB) into single- or three-phase alternating current energy.
[0002] The design features of uninterruptible power supply units (UPS) for industrial consumers are determined by regulatory requirements for them [1,2,3]:
[0003] - During normal operation (including shutdown), the UPS shall provide continuous uninterruptible power supply to all connected loads, including non-linear loads, within the specified tolerances for voltage, waveform and frequency for all types of load expected during operation, including emergency events.
[0004] - When power is lost on the input feeder, the UPS shall supply AC loads for a specified minimum time without the output feeder voltage deviating beyond the specified tolerances.
[0005] - UPS must withstand 2-fold static overload for 1 min and 4-fold for 100 ms [2].
[0006] In accordance with [3], the nominal DC voltage at the UPS input is 110 or 220 V, and the AC voltage at the output is 400 V with a frequency of 50 (400) Hz for 3-phase UPS and 230 V with a frequency of 50 (400) Hz for single-phase UPS, which requires the installation of transformers for voltage matching, as well as galvanic isolation of the consumer network from the circuits associated with the UPS.
[0007] Modern UPSs typically consist of separate systems: a direct current (DC) power supply system with batteries and chargers (rectifiers) and an alternating current (AC) power supply system with inverters and transformers that supply AC loads (Fig. 1).
[0008] In this case, rectifiers are usually thyristor-based, while modern inverters are transistor-based with pulse-width modulation (PWM) based on insulated gate bipolar transistors (IGBT-Insulated Gate Bipolar Transistors), generating a sinusoidal output current.
[0009] Recently, a two-stage UPS design (Fig. 2) has been used to improve weight and size. It consists of a DC / DC converter with intermediate frequency conversion, followed by a width-modulated converter that generates a sinusoidal output voltage. Energy conversion here is threefold. A high-frequency transformer provides potential isolation and coordinates voltage levels. This two-stage structure is an effective technical solution that meets the current state of the art. It allows for a significant weight reduction compared to circuits with 50-Hz transformers. This design is currently finding increasing use. However, high-power UPSs consisting of separate systems (charger, battery, inverter) remain in demand.
[0010] Standard inverter circuits, both single-stage and two-stage designs, have a significant drawback that reduces the efficiency of inverters: the operating current at any given time passes through two series-connected transistors, causing the maximum possible conductive power losses in each of them.
[0011] Two-stage structures, shown in Fig. 2, have a high expected failure rate because the number of sensor elements and connections is significantly greater than in separate structures. Considering that the inverter output is connected to a branched load circuit with numerous elements and connections without isolation, the expected failure rate is further increased by the increased likelihood of the most common types of faults at stations—ground faults.
[0012] The objective of the present invention is to develop a new UPS inverter circuit that reduces the current load and conductive losses in the transistors by almost half. A three-phase version of the proposed circuit is shown in Fig. 3. It includes:
[0013] - two three-phase bridges VZ0 and VZ1, the configuration of which matches the Larionov bridge circuit, composed of transistors with shunt reverse diodes;
[0014] - three-winding transformer T1 with star / reverse star connection of the valve windings with the neutral of the valve windings brought out;
[0015] - constant voltage capacitor bank (CB).
[0016] The DC voltage poles of the KB and the pair of valve bridges are connected.
[0017] The AC voltage poles of the first bridge are connected to the star-connected transformer rectifier winding, and the AC voltage poles of the second bridge are connected to the reverse-star-connected transformer rectifier winding. Battery AB is inserted into the gap between the combined neutral of the rectifier windings and one of the combined DC voltage poles. In Fig. 3, the positive pole of AB is connected to the combined positive pole of the rectifier bridges, and the negative pole of AB is connected to the combined neutral of the rectifier windings. An equivalent option is to connect the negative pole of AB to the combined negative pole of the bridges. In this case, the positive pole of AB is connected to the combined neutral.
[0018] In cases where a three-phase voltage system is not required, a single-phase UDShM, shown in Fig. 4, can be used. It requires only two transistor-diode arms, which together form a single-phase bridge. The transformer here is also a three-winding one, with forward and reverse valve windings. The connections are the same as in a three-phase circuit.
[0019] Despite the similarity between the UDShM circuit and the Larionov bridge circuit, the UDShM circuit is new, as the configuration, valve switching algorithms, and control algorithms differ significantly. Unlike a traditional bridge circuit, the valve switching is implemented in such a way that the battery current is distributed in one half-cycle across two valves of the anode group, and in the other, across two valves of the UDShM circuit's cathode group. As a result, using the UDShM circuit instead of a full bridge circuit almost halves the valve current and, at the same time, reduces conductive energy loss in the valves and their heating. The voltage across the valves doubles, so the UDShM circuit is primarily used in low-voltage power supplies, where doubling the valve voltage is insignificant and has virtually no impact on the choice of component base. These include, in particular, power supplies with batteries rated for 220 and 110 V DC.A comparative analysis of the proposed UDShM circuit and known bridge circuits, as well as the lack of a description of a similar device, allows us to conclude that the proposed technical solution meets the "novelty" criterion. The claimed device is characterized by a combination of features exhibiting new qualities, which allows us to conclude that it meets the "inventive step" criterion.
[0020] A natural alternative to the UDShM is the use of full bridge circuits: three-phase (Larionov bridge, three pairs of valves) or single-phase (two pairs of valves).
[0021] However, in these devices, the load currents are always closed through two series-connected valves. The loop voltage drops of the valves are doubled, and with them, the conductive power losses also double. This defect cannot be significantly mitigated even by paralleling bipolar transistors such as IGBTs, since the current-voltage characteristic of a connected IGBT has a dominant initial bias of 0.9-1.1 V, and the total losses in two parallel IGBTs with half the current are practically no less than those in a single IGBT with full current.
[0022] The operating principle of the UDShM can be conveniently considered from its single-phase design. A simplified equivalent circuit diagram of a single-phase UDShM is shown in Fig. 5,a. The leakage inductance between the valve half-windings and the magnetizing current of the transformer are assumed to be negligible. After bringing the network side to the valve side, the circuit shown in Fig. 5,b is obtained, with a two-winding ideal transformer (IT), leakage inductance ls between the valve winding and the network winding, smoothing inductance ld and a capacitor for double voltage. Potentials u0(⋅), u1(⋅) are regulated by high-frequency pulse-width modulation (PWM) so as to obtain the required currents is(⋅), id(⋅). Each variable x(t) of the PWM system consists of two components [4]: a smoothed base and rapidly alternating pulsation :
[0023] x(t)= (t)+ (t). (1)
[0024] Locally averaged components of u 0,1(Basics) represent the required output variables, which can vary according to the task in the range of 0.2d (where d is the battery voltage). Rapidly alternating pulsations are filtered by the PWM filter at the inverter output. The equation for the voltage bases is:
[0025] u0=us / 2+d, (2)
[0026] u1=-us / 2+d.
[0027] Equations for the fundamentals of inflowing currents:
[0028] iu0=is-id / 2, (3)
[0029] iu1=-is-id / 2.
[0030] The filling of the pulse width modulation cycles of the transistor arms s0, s1, determined by the ratio of the output voltage to the source voltage [4], is obtained here from (2) by dividing by 2⋅d:
[0031]
[0032]
[0033] s0, s1 are also locally averaged values of switching variables and reference levels of control system modulators.
[0034] The reduced amplitude of the sine wave of the output voltage of the UDShM can reach the level of 2⋅d
[0035] us(θ)=Us⋅cos(θ), Us≤2⋅d, (5)
[0036] where: Us is the output voltage amplitude; θ=ωt; ω=2π⋅f; f is the network frequency.
[0037] In this case, both fillings s0, s1 remain within the acceptable range
[0038] 0≤s 0,1 (θ)≤1 (6)
[0039] If the battery current is kept constant
[0040] i d (θ)≡Id, (7)
[0041] that is, with a sinusoidal mains voltage and a sinusoidal current with amplitude I s :
[0042] us(θ)=Us⋅cosθ;
[0043] i s (θ)=I s ⋅cos(θ-ϕ), (8)
[0044] potentials u 0,1 , inflowing currents iv 0,1 , as well as filling s 01 , are simply shifted sinusoids. The voltage offset is the battery voltage d. The current offset is determined by the power balance.
[0045] Ps=Pd=Id⋅2d;
[0046] Ps= 1 / 2⋅Us⋅Is⋅cos (ϕ),
[0047] from where it follows
[0048]
[0049] The nominal reduced amplitude Us is determined by the minimum battery voltage. For a battery with a voltage of 220 V
[0050] Us=220⋅0.9=198 V.
[0051] With a small margin, the voltage scale is taken equal to
[0052] Mν=220⋅0.9⋅0.95=188.1 V. (10)
[0053] In this case, in relative units
[0054] Us=2. (11)
[0055] The amplitude of the sine wave of the mains voltage at a nominal output voltage of 230 V -
[0056] U m =230⋅ =325.3 V.
[0057] Transformer T1 transformation ratio
[0058]
[0059] At the nominal point with the battery charged
[0060] Us=2, Is=1 and cosϕ≅0.87
[0061]
[0062] In this case, the current displacement
[0063]
[0064] A three-phase UDShM is obtained by simply combining three single-phase UDShMs on a three-rod transformer. The typical solution is to create a three-phase four-wire system with a strictly fixed neutral. This system is achieved by connecting the network windings in a star. Pairs of phase transistor arms generate phase network voltages with a 0, 120°, and 240° shift. The transformation ratios and load factors remain generally the same as in the single-phase design.
[0065] The equivalent circuit of a three-phase UDShM is shown in Fig. 6. Width-modulated voltage sources v 0,1,2 and v 3,4,5 , display the action of the left and right transistor bridges; us 0,1,2- sinusoidal phase output voltages. Their ripple is negligible due to the action of PWM filters. The AC filtering inductances l are formed by the leakage inductances between the line windings and the valve windings. The DC smoothing inductances ld can also be formed by the leakage inductances between the valve half-windings. For this purpose, they must be spaced so as to ensure the required short-circuit reactance of the half-winding.
[0066] The phase cells of the three-phase angle grinder are modulated with a regular shift of the support saws by 120°
[0067]
[0068] where: pil - PWM support saw;
[0069] pl k (t) - reference saws of PWM phase cells;
[0070] h - half-cycle PWM.
[0071] The circuit operates not as a pair of three-phase bridges, but as a triple of single-phase bridges. At the output, the three phase cells operate as individual single-phase UDShMs, as discussed above. At the same time, the load on the common unit—the capacitor bank Cd—is radically reduced. With a symmetrical three-phase load, the base of the bank current ic(⋅) becomes identically zero at all points along the output sinusoid.
[0072] ∀θ:Îc(t)=0.
[0073] For applications where low failure rates are crucial, UDShM-type circuits are preferable. As noted above, a two-stage system significantly increases the number of sensor elements and connections, which in itself increases the expected failure rate. Even more significant is the fact that a two-stage structure connects a branched circuit with numerous elements and connections to the output without isolation. This increases the likelihood of the most common faults—ground faults. Therefore, despite its lower weight compared to a two-stage structure, the UDShM-type circuit is still suitable. Regarding size and power loss, a two-stage system offers no advantages and may even be inferior to a UDShK.
[0074] Sources of information
[0075] 1. GOST R IEC 61225-2021. "Nuclear power plants. Monitoring, control, and power supply systems. Requirements for static uninterruptible power supply systems of direct and alternating current." Moscow, Standartinform, 2021. - 26 pp.
[0076] 2. NP087-11. Industry standards. Requirements for emergency power supply systems of nuclear power plants. Moscow, 2013. - 20 p.
[0077] 3. GOST R 58786 - 2019. Electrical equipment for nuclear power plants. OTT. - M., Standartinform, 2020. - 93 pp.
[0078] 4. G.M. Mustafa. Method of approximate analysis of pulse-modulated inverters with sinusoidal output voltage. \ Electrical Engineering, 1987, No. 10. - pp. 2-8.
Claims
1. A doubling width-modulated inverter for high-power static uninterruptible power supply units, consisting of two three-phase transistor bridges, a three-phase three-winding transformer with a star / reverse star connection of the valve windings with an external neutral, a capacitor bank of direct voltage, characterized in that the poles of the alternating voltage of one bridge are connected to the valve winding of the transformer connected in a star, and the poles of the alternating voltage of the second bridge are connected to the valve winding of the transformer connected in a reverse star, wherein the storage battery is connected between the combined neutral of the valve windings and one of the combined poles of the direct voltage of the bridges, and the switching of the valves is carried out in such a way that the current of the storage battery is distributed in one half-period across two valves of the anode group, in the other - across two valves of the cathode group.
2. A doubling width-modulated inverter for high-power static uninterruptible power supply units, consisting of a single-phase transistor bridge, a single-phase three-winding transformer with forward and reverse valve windings, a capacitor bank of direct voltage, characterized in that the AC voltage pole of one transistor-diode arm of the bridge is connected to the forward valve winding of the transformer, and the AC voltage pole of the second transistor-diode arm of the bridge is connected to the reverse valve winding, wherein the storage battery is connected between the combined common point of the valve windings and one of the combined poles of the direct voltage of the bridge, and the switching of the valves is carried out in such a way that the current of the storage battery is distributed in one half-period across two valves of the anode group, in the other - across two valves of the cathode group.